Answer:
Number of carbon, hydrogen, and oxygen atoms in sugar:
C: 12H: 22O: 11Explanation:
1) Given balanced chemical equation:
Sugar(s) + 12O₂(g) → 11H₂O(g) + 12CO₂(g)2) Mass conservation law: in a chemical reaction, the atoms are not created nor destroyed; they recombine to form new substances, so the number of atoms of each kind in the reactants is equal to the number of atoms of the same kind in the products.
3) Balance.
-----------------------------------------------------------------------------------------------------
Atom Products = Reactants
-----------------------------------------------------------------------------------------------------
C 12CO₂ ⇒ 12 = 12 in sugar
-----------------------------------------------------------------------------------------------------
H 11H₂O ⇒ 11 × 2 = 22 = 22 in sugar
-----------------------------------------------------------------------------------------------------
O 12CO₂ ⇒ 12 × 2 = 24 12 × 2 = 24 in O₂ + x in sugar
11H₂O ⇒ 11
----------------------------- --------------------------------------------------
24 + 11 = 35 = 24 + x
----------------------------------------------------------------------------------------------------
Solve for x: 35 = 24 + x ⇒ x = 35 - 24 = 11 ∴ 11 O atoms in sugar
Conclusion:
Number of carbon, hydrogen, and oxygen atoms in sugar:
C: 12H: 22O: 11Tim drives to his brother Casey's house. Given the distance travelled and the time spent, what can Tim calculate about his trip?
A) acceleration
B) density
C) force
D) velocity
3. An airplane increases its speed from 100.0 m/s to 160.0 m/s, at the average rate of 15.0 m/s2. How much time does it take for the complete increase in speed?
By definition of average acceleration,
[tex]\bar a=\dfrac{\Delta v}{\Delta t}[/tex]
[tex]\implies15.0\,\dfrac{\mathrm m}{\mathrm s^2}=\dfrac{160.0\,\frac{\mathrm m}{\mathrm s}-100.0\,\frac{\mathrm m}{\mathrm s}}{\Delta t}[/tex]
[tex]\implies\Delta t=4.00\,\mathrm s[/tex]
Different ______ of an element have different numbers of electrons
Different isotopes of an element have different numbers of electrons.
Explanation:Isotopes are atoms of the same element that have different numbers of neutrons. Since the number of electrons in an atom is equal to the number of protons in the nucleus, isotopes with different numbers of neutrons will have different overall numbers of electrons. For example, carbon-12 and carbon-14 are isotopes of carbon, and carbon-12 has 6 electrons while carbon-14 has 8 electrons.
Isotopes are variants of chemical elements with the same number of protons but different numbers of neutrons. They have various practical applications. For example, radioactive isotopes are used in medicine for imaging and cancer treatment, while stable isotopes are used in tracing chemical reactions, dating archaeological artifacts, and studying geological and environmental processes.
Learn more about Isotopes here:https://brainly.com/question/27475737
#SPJ2
What is the wavelength in nm of a light whose first order bright band forms a diffraction angle of 19.0°, and the diffraction grating has 600.0 lines per mm?
Answer:
What is the wavelength in nm of a light whose first order bright band forms a diffraction angle of 19.0°, and the diffraction grating has 600.0 lines per mm?
543 nm
Explanation:
The wavelength in nm of a light whose first order bright band forms a diffraction angle of 19.0° is 543 nm.
What is wavelength?The wavelength is the distance between the adjacent crest or trough of the sinusoidal wave.
Using Huygen's principle of light, we have an expression
nλ =d sinθ
where, n is the order of maximum
λ is the wavelength of light
d is the distance between the lines on diffraction grating
θ is the angle.
The distance between the lines on diffraction grating is
d = 1 / (600 x 1000) or 0.00000167 m
For first order bright band, n = 1
Then, the wavelength will be
1 x λ = 0.00000167 x sin19.0°,
λ = 0.000000543 m
λ = 543 nm
Thus, the wavelength of the first order bright band is 543 nm .
Learn more about wavelength.
https://brainly.com/question/13533093
#SPJ2
The velocity of a car teduces from 30 km/h as the car approaches a stop sigh. Is this an example of positive or negative accelerationthe
Answer:
The stopping car has negative acceleration.
Explanation:
We know acceleration is the rate of change of velocity. That is
Acceleration(a) = ( Final velocity - Initial velocity )/ Time taken.
Here Final velocity = 0 km/h( car stops) and initial velocity = 30 km/h
So acceleration = (0-30)/time = -30/ time
Time is always positive , so -30/time is negative, so the stopping car has negative acceleration.
Can someone tell me how to find acceleration with only using distance and time? It would be much appreciated
AS S =Vit +1/2 at²
Vi = 0 (as initially an object is at rest when it starts motion)
som
S = 1/2 at²
2S/t² =a ( from this we can find acceleration)
Reducing waste and recycling things are ways to conserve energy. True false
I think the correct answer is true :)
A small increase in aperture will result in
a.small increase in brightness large increase in brightness small decrease in size large decrease in sizea. small increase in brightness
A small increase in aperture will result in a small increase in brightness.
Answer:
large increase in brightness
Explanation:
just trust me.
Incident rays parallel to the principle axis of a concave mirror will reflect _____. parallel to the principle axis through the focal point the same direction as the incident ray through the center of curvature
Answer:
Incident rays parallel to the principle axis of a concave mirror will reflect through the focal point.
Explanation:
Why does the temperature of melting ice not change even though energy is being transferred as heat to the ice? A) The potential energy of the molecules does not change. B) Energy is used to break bonds between molecules in ice. C) The kinetic energy is being converted to chemical energy. Eliminate D) The heat energy is absorbed the by molecules and dissappears
when heat is supplied to the the system then as per law of thermodynamics we can say
[tex]Q = \Delta U + W[/tex]
here we can say that heat is converted into the internal energy of gas and some work is done by the system after absorbing this heat.
So here when ice is melting the energy is supplied to the ice which converts into the internal energy of the ice.
Here this internal energy is used to break the bond of ice molecules so that its phase will convert from solid to liquid
So here we can say this heat or this internal energy as Latent heat of fusion of ice
So its formula is given as
[tex]Q = mL[/tex]
so here correct answer is
B) Energy is used to break bonds between molecules in ice.
The correct answer is B) Energy is used to break bonds between molecules in ice.
When ice melts, it undergoes a phase transition from solid to liquid at a constant temperature, which is 0°C (32°F) for water at standard atmospheric pressure.
During this process, the kinetic energy of the molecules (which is related to the temperature of the substance) does not increase because the added energy is not going into increasing the speed at which the molecules move.
Once all the ice has melted and the phase change is complete, any additional energy transferred as heat will then go into increasing the kinetic energy of the water molecules, resulting in an increase in temperature.
Therefore, the statement that Energy is used to break bonds between molecules in ice correctly explains why the temperature of melting ice does not change even though energy is being transferred as heat to the ice. The other options do not accurately describe the process occurring during the melting of ice:
A) The potential energy of the molecules does change as the ice melts; it increases as the molecules move further apart.
C) Kinetic energy is not being converted to chemical energy; rather, energy is being used to overcome the potential energy associated with the intermolecular forces.
D) The heat energy is not absorbed and then disappears; it is used to break the intermolecular bonds and is stored as potential energy in the separated molecules.
The x-axis of a trajectory represents its _____.
A. latitude
B. longitude
C. height in the vertical direction
D. displacement in the horizontal direction
When the mass on an object increases its gravitational pull __________
A. Stays the same
B. Increases
C. Decreases
The answer is B. Increases and here is why:
The Earth, the Sun, Trees, and basically everything has weight, but why does it have weight? Gravity is why it is hard to lift objects and move around, and the more mass that any object has will be subject to gravity and thus increase its gravitational pull.
The reason that lighting tends to strike bigger and taller objects is simply because the bigger objects draw the electricity in the lightning bolt to themselves due to their increased magnetic and gravitational pulls.
A cat leaps into the air to catch a bird with an initial speed of 2.74 m/s at an angle of 60.0° above the ground. What is the highest point of the cat’s trajectory?
A. 0.19 m
B. 10.96 m
C. 0.58 m
D. 0.29 m
Answer: D. 0.29 m
Explanation:
We will use the following equations to describe the leap of the cat:
[tex]y=V_{o}sin\theta t-\frac{gt^{2}}{2}[/tex] (1)
[tex]V_{y}=V_{oy}-gt[/tex] (2)
Where:
[tex]y[/tex] is the height of the cat
[tex]V_{oy}=V_{o}sin\theta[/tex] is the cat's initial velocity
[tex]\theta=60\°[/tex]
[tex]g=9.8m/s^{2}[/tex] is the acceleration due gravity
[tex]t[/tex] is the time
[tex]V_{y}[/tex] is the y-component of the velocity
Now the cat will have its maximum height [tex]y_{max}[/tex] when [tex]V_{y}=0[/tex]. So equation (2) is rewritten as:
[tex]0=V_{oy}-gt[/tex] (3)
Finding [tex]t[/tex]:
[tex]t=\frac{V_{oy}}{g}=\frac{V_{o}sin\theta}{g}[/tex] (4)
[tex]t=\frac{2.74 m/s sin(60\°)}{9.8m/s^{2}}[/tex] (5)
[tex]t=0.24 s[/tex] (6)
Substituting (6) in (1):
[tex]y_{max}=(2.74 m/s)sin(60\°) (0.24 s)-\frac{(9.8m/s^{2})(0.24 s)^{2}}{2}[/tex] (7)
Finally:
[tex]y_{max}=0.287 m \approx 0.29 m[/tex] (8)
The highest point of the cat’s trajectory, considering the initial speed and angle, is found to be 0.29 m using kinematic equations. Therefore, the correct answer is option D.) 0.29 m.
To find the highest point of the cat's trajectory, we need to focus on the vertical component of the initial velocity and use the kinematic equation for vertical motion.
The initial speed of the cat is given as 2.74 m/s at an angle of 60.0° above the ground.
We first decompose this initial velocity into its vertical component:
Vertical component of velocity(Vy),
Vy = V0 * sin(θ) = 2.74 m/s * sin(60.0°) Vy = 2.74 m/s * (√3/2) Vy ≈ 2.37 m/sAt the highest point of the trajectory, the vertical velocity(Vfy) becomes zero. We use the following kinematic equation to find the maximum height (h):
(Vfy)² = (Vy)² - 2ghSince Vfy = 0 at the highest point of the trajectory:
0 = (2.37 m/s)² - 2(9.81 m/s²)hSolving for h:
h = (2.37 m/s)² / (2 * 9.81 m/s²)h ≈ 0.29 mThus, the highest point of the cat’s trajectory is 0.29 m. The correct answer is D. 0.29 m.
Imagine a leaf floating down a creek (south) at a rate of 6m/s. You walk in the creek towards the leaf (north) at a rate of 2m/s. Relative to the ground, at what rate is the leaf moving?
It depends on what is the reference frame where the velocity of the leaf (6 m/s) is measured.
If it is measured with respect to the creek, then the answer is simply "6 m/s south".
If it is measured with respect to the observer moving toward the leaf, then the velocity of the leaf relative to the ground is actually the sum between the velocity of the leaf relative to the observer (6 m/s south, so 6 m/s) and the velocity of the observer relative to the ground (2 m/s north, so -2 m/s):
[tex]v=v_l +v_o =6 m/s +(-2 m/s)=4 m/s[/tex]
and the direction is south.
While Bob is demonstrating the gravitational force on falling objects to his class, he drops an 1.0 lb bag of feathers from the top of the science building. Determine the distance the bag has traveled after falling for 1.5 seconds assuming it has reach free fall and given the gravitational acceleration of 9.8 m/sec2.
Distance = velocity x time
A)
7.4 m
B)
11 m
C)
15 m
D)
22 m
Answer:
Option B, 11 m is the correct answer.
Explanation:
We have equation of motion , [tex]s= ut+\frac{1}{2} at^2[/tex], s is the displacement, u is the initial velocity, a is the acceleration and t is the time.
In this case u = 0 m/s , t = 1.5 seconds , a = acceleration due to gravity = [tex]9.8m/s^2[/tex], we need to find displacement
Substituting
[tex]s= 0*1.5+\frac{1}{2}*9.8*1.5^2\\ \\ s=11.025m[/tex]
So option B, 11 m is the correct answer.
At take off, a plane flies 100 km north before turning to fly 200 km east. How far is its destination from where the plane took off?
Question 3 options:
300 km
224 km
200 km
173 km
Salmon often jump waterfalls to reach their
breeding grounds.
Starting 3.16 m from a waterfall 0.379 m
in height, at what minimum speed must a
salmon jumping at an angle of 37.6
◦
leave the
water to continue upstream? The acceleration
due to gravity is 9.81 m/s
2
.
Answer in units of m/s.
The problem corresponds to the motion of a projectile (the salmon), with initial speed [tex]v_0[/tex], initial direction [tex]\theta=37.6^{\circ}[/tex] and vertical acceleration [tex]g=9.81 m/s^2[/tex] downward. The two equations which gives the horizontal and vertical position of the salmon at time t are
[tex]S_x (t) = v_0 cos \theta t[/tex] (1)
[tex]S_y (t) = v_0 sin \theta t - \frac{1}{2}gt^2[/tex] (2)
We can solve the problem by requiring Sx=3.16 m and Sy=0.379 m, the data of the problem.
Solving eq.(1) for t:
[tex]t=\frac{S_x}{v_0 cos \theta}[/tex]
And substituting this expression of t into eq.(2), we get the following expression for [tex]v_0[/tex]:
[tex]v_0 =\sqrt{\frac{g S_x^2}{2(tan \theta S_x -S_y)cos^2 \alpha}}[/tex]
And substituting the numbers into the equation, we find
[tex]v_0 = 6.16 m/s[/tex]
Which best describes the relationship between internal energy and thermal energy? Thermal energy is a measure of the internal energy of a substance. Internal energy is a measure of the thermal energy of a substance. Internal energy is the portion of thermal energy that can be transferred. Thermal energy is the portion of internal energy that can be transferred.
Internal energy includes all the energies which are inside the system. It includes kinetic energy, potential energy, chemical energy, nuclear energy and as well as the thermal energy. So, thermal energy is the portion of the internal energy and since, the thermal energy can be transferred from one body to another.
Hence, the answer is "Thermal energy is the portion of internal energy that can be transferred."
The inclusion of every form of energy is known as internal energy. The statement best describes internal energy is that "thermal energy is the portion of internal energy that can be transferred."
What is internal energy?The total energy enclosed by a closed system is known as the internal energy of the system. It includes all forms of energy whether it is mechanical energy or thermal energy.
As per the concept of thermodynamics, "The energy is stored in the form of internal energy, after doing the subsequent amount of work". Moreover, Internal energy includes all the energies which are inside the system. It includes kinetic energy, potential energy, chemical energy, nuclear energy, and as well as thermal energy. So, thermal energy is the portion of the internal energy since thermal energy can be transferred from one body to another.
Thus we can conclude that the statement best describes the internal energy is that "thermal energy is the portion of internal energy that can be transferred."
Learn more about the internal energy here:
https://brainly.com/question/11278589
1. Write the equation relating density (D), mass (M), and volume (V).
density (P) Mass (M) volume (V)
P=M/V
The relation that exists between the density (D), mass (M), and volume (V) body are related as follows -
D = M/V
Density (D), mass (M), and volume (V) of any body represents which properties of a body?
The density (D), mass (M), and volume (V) of any body are use to give information about the physical properties of body.
Given is the density (D), mass (M), and volume (V) of a body.
The following relation exist between the density (D), mass (M), and volume (V) body are related as follows -
density (D) = mass (M) / volume (V)
D = M/V
Density is the measurement of amount of mass per unit volume of the body. Volume is the measurement of total space occupied by the body and mass is the measurement of amount of matter inside body.
Therefore, the relation that exists between the density (D), mass (M), and volume (V) body are related as follows -
D = M/V
To solve more questions on Mass - density relations, visit the link below-
https://brainly.com/question/1554048
#SPJ2
Which of the following physical laws can make a simulated collision seem more realistic?
Motion
Gravity
Fluid dynamics
Thermodynamics
PLease Help!
Larry and Balky set up an experiment to analyze the motion of a marble as it rolled down an incline. They started the marble at the top of the ramp and set up photogates to collect data as the marble rolled down the ramp.
Which graph format would allow Larry and Balky to calculate instantaneous velocity using slope?
A) Velocity on the y-axis, time on the x-axis
B) Distance on the y-axis, time on the x-axis
C) Time on the y-axis, distance on the x-axis
D) Velocity on the y-axis, distance on the x-axis
Answer:
Option A is the correct answer.
Explanation:
The instantaneous acceleration = Change in velocity in velocity/Time taken
The slope of the graph should give instantaneous acceleration.
Slope of a graph = Change in value of Y -axis / Change in values of X -axis
Comparing both the equations
Change in value of Y -axis = Change in velocity in velocity
Change in values of X -axis = Time taken
So velocity values should be on the Y axis and Time values should be on the X axis.
Option A is the correct answer.
A package falls off a truck that is moving at 30 m/s
Neglecting air resistance, the horizontal speed of the package just before it hits the ground is <A) zero. B) less than 30 m/s but larger than zero.
Determine the magnitude of the weight of a 3.0 kg object on earth.
A) 3.0 N
B) 29 N
C) 3.3 N
D) 0.31 N
b 29 newtons
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
have to have a certain amount of letters
Answer:
B) 29 N
Explanation:
Weight is a vector quantity. Weight have both magnitude and direction. The weight of an object is the force of attraction towards the object. it might be gravity or reaction force. The SI unit of weight is Newton . Weight can be can be calculated when you multiply the mass of an object and the gravitational acceleration. The weight of a particular object varies with location but the mass of the an object is same in any location. The weight of an object is measured with a scale.
Since the mass of the object is given , the weight can be calculated.
W = mass × gravitational acceleration
W = mg
m = 3.0 kg
g = 9.8 m/s²
w = 3.0 × 9.8
w = 29.4 N
Anyone taking IB Physics?
Yes, how can I help you?
The IB Physics course, similar to AP Physics, provides high school students with an in-depth introduction to physics at a college level. Though these courses can prove challenging, as evidenced by a 30% withdrawal rate at ABC High School, they cover critical topics of physics and lay the groundwork for more advanced studies.
Explanation:The question asks if anyone is taking IB Physics. The International Baccalaureate (IB) Physics course is similar to the Advanced Placement (AP) Physics course. Like AP Physics, the IB Physics course is a challenging program that provides high school students an in-depth study of physics similar to a college introductory course. However, these courses can be quite demanding, as denoted by the withdrawal rate from an elementary physics course in ABC High School being 30 percent for any given term.
In an IB Physics or AP Physics course, you will cover topics such as mechanics, thermodynamics, waves and sound, light and optics, and nuclear physics. The curriculum promotes depth of understanding over breadth of content, and organizes concepts around seven major themes known as the 'Big Ideas'. Despite a fear amongst many of difficult equations or memorizing formulas, these courses serve as a good foundation for future advanced physics courses at the college level.
Learn more about IB Physics here:
https://brainly.com/question/29560531
#SPJ12
can someone describe how someone is moving-- have examples of positive velocity negative velocity and acceleration and the person being at rest. Can someone help me asap i need Help!! making it into a story
Assume the motion when you are in the car or in the school bus to go to the school.
To describe the motion the first thing you need is a point of reference. Assume this is your house.
This should be a description:
When you are sitting and the car has not started to move you are at rest.The car starts moving from rest, gaining speed, accelerating. You start to move away from your house, with a positive velocity (from you house to your school) and positive acceleration (velocity increases).The car reaches a limit speed of 40mph, and then moves at constant speed. The motion is uniform, the velocity is constant, positive, since you move in the same direction), and the acceleration is zero.When the car approaches the school, the driver starts to slow down. Then, you speed is lower but yet the velocity is positive, as you are going in the same direction. The acceleration is negative because it is in the opposite direction of the motion.When the car stops, you are again at rest: zero velocity and zero acceleration.In all the path your velocity was positive, constant at times (zero acceleration) and variable at others (accelerating or decelerating).When you comeback home, then you can start to compute negative velocities, as you will be decreasing the distance from your point of reference (your house).What's the most often given a value of zero to describe an object position on a straight line
A.Displacement
B.reference point
C.distance
D.ending location
Answer:
Reference point
Explanation:
To explain the position of an object, we have to choose some location or point from where we start to observe the position of the object. This point is called reference point.
As we move leftwards from the reference point, the position of the object is taken as negative and if we move rightwards from the reference point, the position of the object is taken as positive.
Can someone help with these?
6.
Basically, all of these questions use F = ma
m = 80 kg
a = 1.62
Weight = F = 80*1.62 = 129.6
The closest answer is B
7.
Step One
Find the mass here on earth
m = F/a
F = 40 kg
a = 9.2
F = 40/9.2 = 4.34
Now take everything to the moon
F = 20 kg
a = ??
m = 4.34
a = F/m = 20/4.34 = 4.6 m/s^2
8
m = 40 kg
F = 20 N
a = ??
a = F/m = 20N/40kg = 1/2 m/s^2
Comment
All of these depend on F = m*a. None but the first one talk about vertical forces where gravity would play a part. Moving horizontally means that there is no gravitational force if there is no friction. a = 9.8 has nothing to do with the problem.
a rocket is launched with a constant acceleration straight up. exactly 4.00 seconds after lift off, a bolt falls off the side of the rocket and hits the ground 6.00 seconds later. what was the rockets acceleration?
The initial speed of the bolt is not 58.86 m/s.
Let a be the acceleration of the rocket.
During the 4 sec lift off, the rocket has reached a height of
h = (1/2)*a*t^2
with t=4,
h = (1/2)*a^16
h = 8*a
Its velocity at 4 sec is
v = t*a
v = 4*a
The initial velocity of the bolt is thus 4*a.
During the 6 sec fall, the bolt has the initial velocity V0=-4*a and it drops a total height of h=8*a. From the equation of motion,
h = (1/2)*g*t^2 + V0*t
Substituting h0=8*a, t=6 and V0=-4*a into it,
8*a = (1/2)*g*36 - 4*a*6
Solving for a
a = 5.52 m/s^2
While Bob is demonstrating the gravitational force on falling objects to his class, he drops an 1.0 lb bag of feathers from the top of the science building. Determine the distance the bag has traveled after falling for 1.5 seconds assuming it has reach free fall and given the gravitational acceleration of 9.8 m/sec2.
A) 7.4 m
B) 11 m
C) 15 m
D) 22 m
The 1.0 lb bag of feathers, dropped under free fall conditions from the building, would have fallen approximately 11 meters after 1.5 seconds, according to the physics formula for distance traveled during free fall. The correct answer is (B) 11 m.
Explanation:In this problem, Bob is examining the gravitational force acting on a falling object, specifically a 1.0 lb bag of feathers. To determine the distance the feathers have fallen after 1.5 seconds under free fall conditions, we utilize the physics formula for distance traveled during free fall, represented as d = 0.5 * g * t^2, where d is the distance, g is the gravitational acceleration (9.8 m/sec2), and t is the time.
Substitute the given values into the equation, you get d = 0.5 * 9.8 * (1.5)^2. After calculating, it results in approximately 11 meters. Therefore, the bag of feathers has fallen 11 meters after 1.5 seconds, assuming it has reached free fall. This implies that the correct answer is (B) 11 m.
Learn more about Gravitational Force here:https://brainly.com/question/32609171
#SPJ12
The bag has traveled approximately 7.4 meters after falling for 1.5 seconds.
Explanation:To determine the distance the bag has traveled after falling for 1.5 seconds, we can use the equation of motion d = ½gt^2, where d is the distance, g is the gravitational acceleration, and t is the time.
Given that the gravitational acceleration is 9.8 m/sec^2 and the time is 1.5 seconds, we can substitute these values into the equation to calculate the distance:
d = ½ × 9.8 × (1.5)^2
Simplifying the equation, we have:
d = 0.5 × 9.8 × 2.25 = 7.425 m
Therefore, the bag has traveled a distance of approximately 7.4 meters after falling for 1.5 seconds.
Learn more about distance traveled here:https://brainly.com/question/29055485
#SPJ12
A boy and his skateboard have a combined mass of 65 kg. What is the speed of the boy and skateboard if they have a momentum of 275 kg • ? 0 m/s 0.24 m/s 4.2 m/s 8.5 m/s
Answer : Speed is 4.2 m/s
Explanation :
The combined mass of the boy and the skateboard is 65 kg
The momentum of the boy and the skateboard is 275 kg m/s
The momentum is given by:
p = m v
where m is the combined mass of boy and the skateboard.
v is the speed of both boy and the skateboard.
[tex]v=\dfrac{p}{m}[/tex]
[tex]v=\dfrac{275\ kg\ m/s}{65\ kg}[/tex]
[tex]v=4.23\ m/s[/tex]
The speed of the boy and the skateboard is 4.2 m/s
So, the correct option is (C).
Hence, this is the required solution.