CAIE A-Level Physics 3.3.4 Momentum and Kinetic-Energy Changes

Practise conserving system momentum while calculating kinetic-energy transfers in inelastic interactions.

[Maximum number: 3]

Ball A moves with speed v along a horizontal frictionless surface towards a stationary ball B, as shown in Fig. 3.1.

Fig. 3.1

Ball A has mass 4.0 kg and ball B has mass 12 kg .
The balls collide and then move apart as shown in Fig. 3.2.
Ball A has velocity $6.0 \mathrm{~ms}^{-1}$ at an angle of $\theta$ to the direction of its initial path.
Ball B has velocity $3.5 \mathrm{~ms}^{-1}$ at an angle of $30^{\circ}$ to the direction of the initial path of ball A.

By calculation of kinetic energies, state and explain whether the collision is elastic or inelastic.

initial $E_{\mathrm{K}}\left(=1 / 2 \times 4.0 \times 12^{2}\right)=290(288)(\mathrm{J})$

M1

final $E_{\mathrm{K}}\left(=1 / 2 \times 4.0 \times 6.0^{2}+1 / 2 \times 12 \times 3.5^{2}\right)=150(145.5)(\mathrm{J})$

M1

(initial $E_{\mathrm{K}}>$ final $E_{\mathrm{K}}$ ) so inelastic [both M1 marks required to award this mark]

A1

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3.3.4—That, while momentum of a system is always conserved in interactions between question 1