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UPSC Civil Service Exam Questions - Engineering

Q1:

Two particles of masses 21 gm and 28 gm are connected by a light inextensible string which passes over a fixed smooth pulley. The tension in the string in the ensuing motion will be

A 7 gm. wt

B 10 gm. wt

C 12 gm. wt

D 24 gm. wt

ANS:D - 24 gm. wt

Let's assume the tension T in the string.
Acceleration a in the string due to different loads,
Consider fbd of 21gm mass.
T-21g = 21a ----> (1)

Considering fbd of 28gm mass
28g - T = 28a ---> (2)
By solving these equations;
a = g/7.
T = 24g.