Question

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/s². the coefficient of friction 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
• C. +500 J
• D. -500 J

Answer 1

Answer: (A)

+250 J

Answer 2

Assuming that the block does not slide on the platform

F_f = ma = 5(1) = 5N ; N – mg = 0

⇒ N = mg = 50 N, As μN = 10 N, F_f < μN

The block will remain at rest relative to the platform. Displacement D relative to the ground = $\frac { 1 } { 2 } ( 1 ) ( 10 ) ^ { 2 }$ = 50 m

∴ Work of friction = F_fD cos 0 = +250 J, Hence, the correct choice is (1).