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Question: Two blocks of masses 2 kg and 5 kg are at rest on ground. The masses are connected by a string passi...

Two blocks of masses 2 kg and 5 kg are at rest on ground. The masses are connected by a string passing over a frictionless pulley which is under the influence of a constant upward force F = 50 N. The accelerations of 5 kg and 2 kg masses are

A

0,2.5 ms-2

B

0,0

C

2.5 ms-2,2.5 ms-2

D

1 ms-2 2.5 ms-2

Answer

0,2.5 ms-2

Explanation

Solution

The masses will be lifted if the tension of the string is greater than the gravitational pull on masses.

Weight of 5 kg mass = 5 × 10 = 50 N and 2 kg mass = 2 × 10 = 20 N

From free body diagram

50 – 2T = 0 or T = 25 N

So 5 kg weight can not lifted ( acceleration = 0)but 2 kg weight will be lifted.

∴25 – 20 = 2a or a = 52=2.5 ms−2\frac { 5 } { 2 } = 2.5 \mathrm {~ms} ^ { - 2 }