A worker pushes a box in a factory. In each case, decide which force has the greater magnitude: the force exerted by the worker on the box or the force exerted by the box on the worker.

Part A

The box is heavy and does not move no matter how hard the worker pushes.

A)The force exerted by the worker on the box is greater.

B)The magnitudes of the forces are equal.

C)The force exerted by the box on the worker is greater.

Part B

Some contents are removed, and now when pushed the box slides across the floor at constant speed.

A)The force exerted by the worker on the box is greater.

B)The magnitudes of the forces are equal.

C)The force exerted by the box on the worker is greater.

Part C

The worker pushes harder, and the box accelerates.

A)The magnitudes of the forces are equal.

B)The force exerted by the worker on the box is greater.

C)The force exerted by the box on the worker is greater.

B)The magnitudes of the forces are equal.

B)The magnitudes of the forces are equal.

A)The magnitudes of the forces are equal.

Explanation:

A.

B)The magnitudes of the forces are equal.

The force exerted on the box and it does not moves means that the static frictional force on the box is enough to stop the box from motion.

As the applied force increases the force of friction also increases. This happens until the friction value reaches its limiting point called the limiting frictional force.

B.

B)The magnitudes of the forces are equal.

Now when the box becomes lighter when some contents are removed and hence the normal force is reduced which further reduces the effective frictional force.

But the force applied on the box is equal to the force applied by the box on the worker it is just that the frictional force between the ground and the worker is large enough to resist its motion.

where:

frictional force

coefficient of friction between the surfaces

N = normal force to the contact surface

C.

A)The magnitudes of the forces are equal.

When the box accelerates there is change in velocity of the box.

But the force applied on the box is equal to the force applied by the box on the worker it is just that the frictional force between the ground and the worker is large enough to resist its motion.