devarshi-dt-logo

Question:

A body of mass 2kg slides down with an acceleration of 3m/s² on a rough inclined plane having a slope of 30°. The external force required to take the same body up the plane with the same acceleration will be:(g=10m/s²)

20N

14N

4N

6N

Solution:

Equation of motion when the mass slides down
Mgsinθ - f = Ma
10 - f = 6
f = 4N
Equation of motion when the block is pushed up
Let the external force be F
F - Mgsinθ - f = Ma
F - 10 - 4 = 6
F = 20N