Question

A 75 kg girl running at 3.0 m/s jumps onto a sled that has a mass of 10 kg and that is already moving in the same direction as the girl, at 2.0 m/s. What will be the final velocity of the girl and the sled,
assuming that the sled is on level snow and that there is no friction.

A 100 g ball moving at a constant velocity of 200 cm/s strikes a 400 g ball that is at rest. After the collision, the first ball rebounds straight back at 120 cm/s. Calculate the final velocity of the second ball.

Will give medals, please help. I do not fully understand what it's asking or the formula to use.

Answer 1

For the first part, use the equation for an inelastic collision:
\[m _{1}v _{1}+m _{2}v _{2}=(m _{1}+m _{2})v _{3}\]
Plug in the given values of mass and velocity and solve for the velocity v_3 for the girl + sled

Answer 2

for the second part use the equation for an elastic collision:
\[m _{1}v _{i1}+m _{2}v _{i2}=m _{1}v _{f1}+m _{2}v _{f2}\]
Plug in the given values and solve for the final velocity of the second ball v_f2