Question
Question: Two blocks A and B of mass 2 kg and 4 kg are placed one over the other. A horizontal force F = 2t, w...
Two blocks A and B of mass 2 kg and 4 kg are placed one over the other. A horizontal force F = 2t, which varies with time is applied on the upper block. If coefficient of friction between blocks A and B is 0.5 and horizontal surface is smooth. Then assuming t is in seconds, the total time upto which both blocks will move together without slipping over each other is –
A
5 sec
B
7.5 sec
C
10 sec
D
12.5 sec
Answer
7.5 sec
Explanation
Solution
If common maximum acceleration is a then,
(mA + mB)a = f
(2 + 4)a = 2t
3a = t … (1)
For block B
fL = mB × a
0.5 × 2 × 10 = 4a
a = 2.5 m/s2
From equation (1)
t = 7.5 sec