During an ice skating event, two partners (a 60.0kg boy and a 45.0 kg girl) push

Question

During an ice skating event, two partners (a 60.0kg boy and a 45.0 kg girl) pushed away from each other. Before they came into contact, the girl was moving toward the boy with a speed of 3.00m/s. The move was timed perfectly, so that after they pushed off they moved in opposite directions, each with the same speed of 3.00m/s. Before and after they pushed off, the boy and girl only moved forward or backward along the same line as the initial velocity of the girl. You should assume that during the time that the two were in contact, friction was small enough to be ignored.

1) Using only the information you have been provied thus far, ignore alll sources of friction and external forces, and find the velocity of the boy before the two skaters pushed off each other.

2) Now you are give the additional piece of information that they pushed off with their hands for one and a half seconds (1.50s). You may use this piece of information for the rest of this question (through part f). Find the average acceleration of the girl during the time the two were in contact.

3) Ignoring all sources of friction and external forces, find the magnitude of the average force that the boy exerted on the girl during the time they were in contact.

4) Ignoring all sources of friction and external forces, find the magnitude of the average force that the girl exerted on the boy during the time they were in contact.

5) Find the average acceleration of the boy during the time the two were in contact.

6) Compare the magnitudes of your previous four answers:

a) How does the magnitude of your answer to part b compare to the magnitude of your answer to part c? If they are the same explain what principle causes them to be the same. If they are different explain what priciple causes them to be different

b) How does the magnitude of your answer to part a compare to the magnitude of your answer to part d? If they are the same explain what principle causes them to be the same. If they are different explain what principle cuases them to be different?

Explanation / Answer

1) momentum

45*3 + 60*v = 45*-3 + 60*3

v=-1.5 m/s

2)

F = dp/dt

F = m dv/dt

F = ma

so a = dv/dt = (-3 -3)/1.5 = -6/1.5 = -4 m/s^2

3) F = ma = 45*4 = 180 N

4) newtons third law

F girl = F boy

so F = 180 N

5)

a = F/m = 180/60 = 3 m/s^2

6)

a) they are the same since newtons third law

b) different since different masses

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