Two friends, Al and Jo, have a combined mass of 183 kg. At the ice skating rink,

Question

Two friends, Al and Jo, have a combined mass of 183 kg. At the ice skating rink, they stand close together on skates, at rest and facing each other. Using their arms, they push on each other for 1 second and move off in opposite directions. Al moves off with a speed of 7.5 m/sec in one direction and Jo moves off with a speed of 6 m/sec in the other. You can assume friction is negligible.

ONLY #3 AND #4

1) 81

What is Al's mass?

kg

2) 101.66

What is Jo's mass?

kg

3)

If you assume the force is constant during the 1 second they are pushing on each other, what is the magnitude of the force of Al on Jo?

N  

Help:

You know the initial velocity of Jo before the push and you know his final velocity after the push. What is his acceleration?

4)

If you assume the force is constant during the 1 second they are pushing on each other, what is the magnitude of the force of Jo on Al?

N  

Help:

You know the initial velocity of Al before the push and you know his final velocity after the push. What is his acceleration? How should the force of Joe on Al, and the force of Al on Joe, be related?

Explanation / Answer

1)

according to conservation of momentum

m1u1+m2u2=m1v1+m2v2

Mv - mV = (M + m)v0 = 0 from the conservation of momentum; so M = mV/v where M = big person mass, m = small person mass, V = small person velocity, v = big person velocity. v0 = the velocity of the M + m two masses while together, which is zero.

M=m*7.5/6

M=1.25m

M+m=183

m=183/2.25

=81.33kg

2)

M=183-81.33

=101.66kg

3)

force is constant during the 1 second they are pushing on each other

accelration of al=v/t

=7.5m/s2

F=81.33*7.5

=609.975N

4)

a=6m/s2

F=101.66*6

=609.96N

they are exerting equal and opposite forces net force equal to zero

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