A block of mass 1 kg is pushed up a surface inclined to horizontal at an angle of `30^@` by a force of 10 N parallel to the inclined surface as shown in the figure.
The coefficient of friction between block and the incline is 0.1. If the block is pushed up by 10 m along the incline, then the work against gravity is (Take `g=10 m s^(-2 )`)

Options

A. 8.7 J
B. 10.7 J
C. 7.8 J
D. 12.7 J

Answer

A

Explanation

Work against friction is
` W_(f ) = fd = mu Nd = mu m g d cos theta ( therefore N = mg cos theta )`
`=0.1 xx 1 Kg xx 10 ms- 2 xx cos 30 ^(@) xx 10 m`
`= 8.7 J `