A plank of mass m 1 = 8 kg with a bar of mass m 2 = 2 kg placed on its rough surface, lie on a smooth floor of elevator ascending with an acceleration g/4. The coefficient of friction is µ = 1/5 between m 1 and m 2 . A horizontal force F = 30 N is applied to the plank. Then the acceleration of bar and the plank in the reference frame of elevator are:
A
3.5 m/s 2 , 5 m/s 2
B
5 m/s 2 , 
m/s 2
m/s 2
C
2.5 m/s 2 , 
m/s 2
m/s 2
D
4.5 m/s 2 , 4.5m/s 2
Text Solution
Verified by ExpertsThe correct answer is:
C
Solving from the frame of elevator
g eff. = g + 
= 12.5
(Relative slipping occurs)
f = 
× 2 × 12.5 = 5N
a 2 = 
= 2.5 m/s 2 
a 1 = 
= 
m/sec
2
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