A) kinetic energy
B) momentum
C) potential energy
D) kinetic energy and momentum
Correct Answer: D
Solution :
A collision is said to be elastic if the total kinetic energy before and after collision remain the same or KE is conserved. Thus, if two bodies of masses \[{{m}_{1}}\]and \[{{m}_{2}}\]moving with velocities \[{{u}_{1}}\] and \[{{u}_{2}}\]collide in absence of external force also elastically and \[{{v}_{1}}\]and \[{{v}_{2}}\]are the final velocities, then according to conservation of momentum \[{{m}_{1}}{{u}_{1}}+{{m}_{2}}{{u}_{2}}={{m}_{1}}{{v}_{1}}+{{m}_{2}}{{v}_{2}}\] Also, according to principle of conservation of KE \[\frac{1}{2}mu_{1}^{2}+\frac{1}{2}mu_{2}^{2}=\frac{1}{2}mv_{1}^{2}+\frac{1}{2}mv_{2}^{2}\] Therefore, it is clear that both kinetic energy and momentum are conserved.
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