An interacting system of two objects has no external force acting on the system. The first has a mass of 2.00kg and is moving with a velocity (2.00m/s)i + (1.00m/s)j at time t=0s. The second object has a mass of 3.00kg and is moving with a velocity (-1.00m/s)i + (1.00m/s)j at time t=0s. The second object is moving with a velocity (2.00m/s)i +(-1.00m/s)j at time t=1s.

Question

A. what is the total momentum of the system at time t=0s?
B. what is the velocity of the first object at t=1s?

Answer 1

initially
p1 = 4 i + 2 j
p2 = -3i + 3 j
total p = 1 i + 5 j

final p must be the same

final
p1 = px i + py j
p2 = 6 i - 3 j

px + 6 = 1
px = -5
vx = -5/2 = -2.5

py -3 = 5
vy = 5/2 = 2.5

so
v = -2.5 i + 2.5 j