Question

A friction trolley is pushed from rest with a force of 40N for 15s. It strikes a wall and comes to rest in 0.2s. Compute the average force that the wall exerted on the trolley.

Answer 1

The momentum initially given to the trolley is:

$$p = F_1t_1$$

where $F_1 = 40N$, and $t = 15s$. The wall took all this momentum in $t_2 = 0.2s$. Thus, the average force exerted on the trolley is:

$$F_2 = \dfrac{p}{t_2} = \dfrac{F_1t_1}{t_2}\\ F_2 = \dfrac{40\cdot 15}{0.2} = 3000N$$

Answer. 3000 N.