Question

A child pulls a block across the floor with force applied by a horizontally held string. A smaller frictional force also acts upon the block yielding a net force on the block that is smaller than the force applied by the string. How does the work done by the string compare with the change in the block’s kinetic energy?

Answer 1

Answer:

work done by tension force is more than the change in kinetic energy of the block

Explanation:

As we know that by work energy theorem we know that

Work done by all forces on the system must be equal to the change in kinetic energy of the system

so here when a block is pulled horizontally by applied tension force on the rope and there exist some frictional force on it

so we can say that net work done on the block must be equal to change in kinetic energy of the system

So we have

$W_f + W_T = \frac{1}{2}m(v_f^2 - v_i^2)$

$W_T - W_f = \Delta K$

so we have

$W_T = W_f + \Delta K$

So here we can see that since work done by frictional force is always negative so work done by tension force is sum of work done by frictional force and change in kinetic energy.

So work done by tension force is more than the change in kinetic energy of the block