IB Physics HL A.2.22 Kinetic Energy in Collisions

Practise analysing HL kinetic-energy loss in multi-body collisions and interpreting energy-transfer evidence.

Exam points

compare kinetic energy and momentum in elastic collisions, inelastic collisions and explosions
use momentum conservation to identify energy lost or gained in a collision or explosion
interpret before-and-after speeds and masses to justify the collision-energy classification

[Maximum number: 3]

A horizontal rigid bar of length 2 R is pivoted at its centre. The bar is free to rotate in a horizontal plane about a vertical axis through the pivot. A point particle of mass M is attached to one end of the bar and a container is attached to the other end of the bar.

A point particle of mass $\frac{M}{3}$ moving with speed v at right angles to the rod collides with the container and gets stuck in the container. The system then starts to rotate about the vertical axis.

The mass of the rod and the container can be neglected.

Figure for Question A.2.22—Collision energy question 1 — IB Physics HL

Determine in terms of M and v the energy lost during the collision.

$\text { initial } K E=\frac{M v^{2}}{6}$

final $K E=\frac{M v^{2}}{24}$

energy loss $=\frac{M v^{2}}{8}$

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A.2.22—Collision energy question 1