A mass of 1kg is just able to slide down the slope of an inclined rough surface when the angle of inclination is `60^@`. The minimum force necessary to pull the mass up the inclined plane is

Options

A. 14.14N
B. 17.32N
C. 10N
D. 16.66N

Answer

B

Explanation

The component of weight mg of block along the inclined plane =`mg sin theta`. The minimum frictional force to be overcome is also `mg sin theta`. To make the block just move up the plane the minimum force applied must overcome the component `mg sin theta` of gravitional force as well as the frictional force `mg sin theta= 2 mg sin theta`
`therefore` Force needed= `2 mg sin theta`
`=2 times 1 times 10 times sin 60^@`
`=20 times sqrt3/2`
`=17.32 N`