Question

A block of mass 1 kg is pushed up a surface inclined to horizontal at an angle of $30 ^ { \circ }$ 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 done against force of friction is :

(Take $\mathrm { g } = 10 \mathrm {~ms} ^ { - 2 }$)

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

Answer 1

Answer: (A)

8.7 J

Answer 2

Work against friction is

$\mathrm { W } _ { \mathrm { f } } = \mathrm { fd } = \mu \mathrm { Nd } = \mu \mathrm { mg } \cos \theta \mathrm { d }$ $( \therefore \mathrm { N } = \mathrm { mg } \cos \theta )$

= 8.7J