A9.13e+3 kg railroad car is rolling at 3.15 m/s when a 4.20e+3 kg load of gravel is suddenly dropped in from directly above. what is the car's speed immediately after the gravel is dropped in?

6.85 m/s

Explanation:

We can solve the problem by using the law of conservation of momentum.

In fact, since there are no external forces acting, the total momentum before and after must be conserved. So we can write:

where

is the initial mass of the car

is the initial speed of the car

is the mass of the car after the load of gravel is dropped

v2 is the final speed of the car

Solving for v2, we find