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Two bodies A and B of masses 5 kg and 8 kg are moving such that the momentum of body B is twice that of body A. The ratio of their kinetic energies will be

Asked in JEE Main 30th June 1st Shift 2022 · Relating kinetic energy to momentum

• (1) 4 : 5
• (2) 2 : 5
• (3) 5 : 4
• (4) 5 : 2

Step-by-step solution

Why the other options are wrong

• (1) Comes from forgetting to square the momentum ratio, K∝ p/m: (p/5)/(2p/8)=4/5.
• (3) Comes from K∝ p/m with the ratio taken as B:A: (2p/8)/(p/5)=5/4.
• (4) Comes from inverting the ratio: this is K_B:K_A.

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