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° 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 \[F=w\text{ }sin\text{ }\theta \] \[=mg\text{ }sin\text{ }{{15}^{o}}\]                                                 \[=2sin\,{{15}^{o}}\]                                                 \[=0.5176\text{ }kN\] Also, work done = force \[\times \] displacement                 \[=0.5176\times 10=\text{ }5.17\text{ }kJ\]