CAIE A-Level Physics AS 3.3.4 That While Momentum of a System Is Always Conserved in Interactions Between Questions

Distinguish conservation of momentum from conservation of kinetic energy in interactions between objects.

Exam points

Distinguish conservation of momentum from conservation of kinetic energy in interactions between objects.

[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 $E_{\mathrm{K}}\left(=1 / 2 \times 4.0 \times 12^{2}\right)=290(288)(\mathrm{J})$
final $E_{\mathrm{K}}\left(=1 / 2 \times 4.0 \times 6.0^{2}+1 / 2 \times 12 \times 3.5^{2}\right)=150(145.5)(\mathrm{J})$
(initial $E_{\mathrm{K}}>$ final $E_{\mathrm{K}}$ ) so inelastic [both M1 marks required to award this mark]

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CAIE A-Level Physics AS 3.3.4 That While Momentum of a System Is Always Conserved in Interactions Between Questions question 1