a 5 kg block is kept on a horizontal platform at rest. at time t = 0, the platform starts moving with a constant acceleration of 1 m/s 2 . the coefficient of friction μ μ between the block and the platform is 0.2. the work done by the force of friction on the block in the fixed reference frame in 10 s is
( a ) +250 J ( b ) -250 J
Text Solution
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Assuming that the block does not slide on the platform
F f = ma = 5(1) = 5N; N – mg = 0
⇒ ⇒ N = mg = 50 N, As μ μ N = 10 N, F f < μ μ N
The block will remain at rest relative to the platform. Displacement D relative to the ground = 
= 50 m
∴ ∴ Work of friction = F f D cos 0 = +250 J, Hence, the correct choice is .
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