question_answer 1)

The sign of work done by a force on a body is important to understand. State carefully if the following quantities are positive or negative. (i) Work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket. (ii) Work done by gravitational force in the above case. (iii) Work done by friction on a body sliding down an inclined plane.- (iv) Work done by an applied force on a body moving on a rough horizontal plane with uniform velocity. (v) Work done by the resistive force of air on a vibrating pendulum in bringing it to rest.  

Answer:

(i) Work done is positive, because the bucket moves in the direction of the force applied by the man. (ii) Work done by gravitational force is negative because the bucket moves upwards while the gravitational force acts downwards. (iii) Work done is negative, because force of friction acts on the body in the opposite direction of its motion. (iv) Work done is positive, because the applied force acts in the direction of motion of the body. (v) Work done is negative, because the resistive force of air acts in a direction opposite to the direction of motion of the vibrating pendulum.