A-level · Momentum

Conservation of linear momentumExam-style questions

The principle that the total momentum of a system is unchanged by a direct collision — how to set it up with a consistent positive direction, the special case where the bodies coalesce (stick together) and move with a common velocity, and how to read the sign of the answer as a direction.

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19 questions · A Level level · mark scheme and worked solution on each · no sign-up to try

DifficultyAll Level 2 Level 3 Level 4 Level 5

1
Figure 2Diagram not accurately drawn.

Two small blocks, $A$ of mass $0.6$ kg and $B$ of mass $0.9$ kg, rest $1.25$ m apart on a rough horizontal floor, as shown in Figure 2. The blocks are modelled as particles.

The coefficient of friction between each block and the floor is $\frac{2}{7}$

A sharp blow gives $A$ an impulse of $2.4$ N s, directed towards $B$ , and $A$ starts to slide across the floor.
(a) Find the speed with which $A$ starts to slide.

(2 marks)
(b) Show that $A$ reaches $B$ with speed $3\text{ m s}^{-1}$

(5 marks)

In the collision, $A$ and $B$ join together and move as a single particle.
(c) Find the speed of the combined particle immediately after the collision.

(2 marks)
(d) Find the magnitude of the impulse exerted on $A$ by $B$ in the collision, stating the units of your answer.

(2 marks)
(e) Find the distance travelled by the combined particle after the collision until it comes to rest.

(3 marks)
Level 5 · 14 marksTry it
2
A particle $A$ of mass $3m$ moving with speed $u$ collides directly with a stationary particle $B$ of mass $m$ . After the collision $A$ continues in the same direction with speed $\dfrac{u}{2}$ .
(a) Find the speed of $B$ after the collision, in terms of $u$ . (4 marks)
(b) Explain why the particles do not collide again. (1 mark)
Level 5 · 5 marksTry it