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Momentum Question

Hey, I'm struggling on understanding a question on momentum in my kerboodle book, it goes: A skater of 60kg and 80kg stand in the middle of an ice rink and push apart.
Describe:
a.) what force they exert on each other when they push apart
b.) momentum eachother have after they separate
c.) their velocities after separating
d.) their total momentum

I understand the basic equation for momentum but I'm struggling with this one haha, help would be much appreciated :smile:

Reply 1

Ladkus

Try thinking about Newton's laws of motion for part a

Reply 2

Physics Enemy

Original post by RJM02

Skaters of 60 kg and 80 kg stand in the middle of an ice rink and push apart. Describe:

a.) force they exert on eachother when they push apart
b.) momentum each has after they separate
c.) their velocities after separating
d.) their total momentum

a) They exert equal & opposite push forces on one another, forming an action-reaction pair under Newton's 3rd Law.

b) Pushing from rest, hence equal & opposite momenta: p (80) = - p (60).

c) 80v = -60v* => v = -(3/4)v*. So 80 kg travels at 3/4 speed (velocity mag) of 60 kg, their velocities oppose in direction.

d) Total p (before) = Total p (after) = 0 kg ms^-1. i.e) momentum conserved in the absence of external forces.