Question

Imagine you have just witnessed a small avalanche on a mountain while skiing, and two slushy snowballs just crashed together in a perfectly inelastic collision. They are moving as one larger snowball, as a combined mass. Before the collision, snowball A was 7 kg and had initial momentum of –14 kg · m/s; therefore, its velocity must have been ? m/s
Snowball B had initial momentum of 15 kg ∙ m/s, and a velocity of 5 m/s; therefore, its mass must have been ? kg.

Recognizing that momentum is conserved in inelastic collisions, the total momentum of the combined snowballs after the collision must be ? kg · m/s.

Answer 1

The first is -2.

the second is 3. 

the third is 1. 

Answer 2

We have that the momentum p is given by the formula p=mv where m is the mass and v is the velocity. Since for A p=-14kgm/s and m=7, we have that the velocity is -14/7=-2m/s. Hence its speed is 2 m/s.
For b we have that p=15kgm/s and v=3m/s. Because m=p/v, we have m=3kg.
We also have that the momentum is conserved in this system. Hence, the net sum of the momentum of the 2 snowballs equals the momentum of the single giant ball. Hence, p(total)=p(combined)=-14+15=1kgm/s (momentum is a vector; the positive sign means that it tends to the positive direction).