State Newton’s second law of motion in words.
A constant resultant force $F$ acts on object $A$. The graph shows how the velocity $v$ of $A$ changes with time $t$. The mass of $A$ is $840\,\text{g}$. Calculate the change in momentum of $A$ from $t = 0$ to $t = 4.0\,\text{s}$.
Calculate the value of the force $F$.
The force $F$ is removed at $t = 4.0\,\text{s}$. Object $A$ then moves at constant velocity before colliding with object $B$. Object $B$ starts from rest. Objects $A$ and $B$ stick together and move off with velocity $4.7\,\text{m s}^{-1}$. Use calculations to show that the changes in momentum of $A$ and of $B$ during the collision are equal and opposite.
Explain, using the answers in (i), how Newton’s third law is supported.
Using the speeds of $A$ and $B$, explain whether the collision is elastic.