question_answer

The work done in pulling up a block of wood weighing 2 kN for a length of 10 m on a smooth plane inclined at an angle of \[{{15}^{o}}\] with the horizontal is :

A)  9.82 kJ       

B)  8.91 kJ

C)  5.17 kJ       

D)  4.36 kJ

Correct Answer: C

Solution :

The various forces acting on a block kept on inclined plane are as shown. The force of resistance due to inclination when block is pulled upwards is                 \[F=w\sin \theta \]                 \[=mg\sin {{15}^{o}}\]                 \[=2\sin {{15}^{o}}\]                 = 0.5176 kN Also, work done = force x displacement \[=0.571\times 10=5.17\,kJ\]