Chapter 3, Problem 1AC

According to the definition of mechanical work, pushing on a rock accomplishes no work unless there is _

a. movement.

b. a net force.

c. an opposing force.

d. movement in the same direction as the direction of the force.

To determine

The correct option to complete the statement, “According to the definition of mechanical work, pushing on a rock accomplishes no work unless there is”, from the following options,

1. movement.

2. a net force.

3. an opposing force.

4. movement in the same direction as the direction of the force.

Answer to Problem 1AC

Solution:

Option (d) is correct.

Explanation of Solution

Introduction:

According to the concept of mechanical work, net work is done on an object if it experiences a net force that brings a displacement in the object.

Explanation:

Reason for the correct options:

When direction of applied force and direction of movement are same then only maximum work will be done.

Hence, option (d) is correct.

Reason for the incorrect options:

Option (a) is incorrect because the movement can be perpendicular to the direction of the force. Now if the angle between the force and the displacement is 90 degrees, then the work done comes out to be zero. Hence, it is a wrong option.

Option (b) is incorrect because the presence of net force does not give any information about the displacement of object which is necessary for any work to be done.

Option (c) is incorrect because even if an opposing force is present, there is no movement or there is a movement but at a right angle. So, opposing force doesn’t imply that work is always done. Hence, it is a wrong option.

Hence, options (a), (b) and (c) are incorrect.

Conclusion:

A force will do work on an object only if it has a component in the direction parallel to the motion of the object. Thus, a push on a rock will accomplish work only when the movement of the rock is in the same direction as the direction of the force.