A 2-kg object accelerates as a net external force is applied to it. During the 5

Question

A 2-kg object accelerates as a net external force is applied to it. During the 5-second interval that the force is applied, the object's velocity changes from 3 m/s east to 7 m/s west. A student states: "The change in momentum of this object during these 5 seconds was 8 kg-m/s so the impulse applied to this object during these 5 seconds was 8/5 kg.m/s." What, if anything, is wrong with this statement? If something is wrong, identify and explain how to correct all errors. If this statement is correct, explain why.

Explanation / Answer

let the direction in which the ball was travelling in the beginning be +ve.

initial velocity=+3 m/s

final velocity=-7 m/s

then change in momentum=final momentum-initial momenum

=mass*(final velocity-initial velocity)

=2*(-7-3)=-20 kg.m/s

hence magnitude of change in momentum is 20 kg.m/s along west direction

part b:

as we know, change in momentum=impulse applied*time

==>impulse applied=change in momentum/time

=20/5=4 N

and as the net change in momentum is along west, net impulse is applied along west.

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