A man of mass 80 kg jumps from a trolley of mass 20 kg standing on a smooth surface, with an absolute velocity of 3 m/s. The recoiling speed of the trolley is
A
12 m/s
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B
10 m/s
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C
8 m/s
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D
11 m/s
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Solution
The correct option is A12 m/s Given: Mass of man; m1=80 kg Mass of trolley; m2=20 kg Final velocity of man; v1=3 m/s Initial velocity of man (u1) and trolley (u2) are zero as both are at rest. Let (v2) be the final velocity of trolley.
Considering (man+trolley) as system. As there are no net external force in horizontal direction on the system. ∴ Applying principle of conservation of linear momentum (PCLM) in horizontal direction, m1u1+m2u2=m1v1+m2v2 0=80×3+20×v2 v2=−12 m/s Here negative (- ve) sign shows that trolley moves in the opposite direction of man. ∴Recoiling speed of trolley=12 m/s