Hewitt 4.1-4.2 hw

Whenever a net force acts on an object, there is a change in the object's

• shape.
• velocity.
• direction
• speed

How does acceleration depend on the net force?

• Acceleration is independent of the net force.
• Acceleration is inversely proportional to the net force.
• Acceleration is proportional to the net force.
• Acceleration is equal to the net force.

The direction of the force of friction on a sliding crate is

• usually at right angles to the force that produces sliding.
• non-directional
• in the same direction as the force that produces sliding.
• opposite to the direction of sliding

A crate sits at rest on a factory floor. Friction between the crate and floor occurs

• when the crate is pushed horizontally, whether sliding or not.
• even when no pushing occurs.
• only if the crate is sliding.
• only if the crate is pushed vertically as well as horizontally

When you push horizontally on a crate that doesn't slide on a level floor, how great is the force of friction on the crate?

• The friction force is equal to and in the same direction as your push.
• The friction force is equal and opposite to your push.
• The friction force is zero.
• The friction force is equal to the mass of the crate times its acceleration.

As you increase your push on a stationary crate, will friction on the crate increase also?

• The friction force increases and is opposite in direction to your push.
• The friction force decreases and is in the opposite direction as your push.
• The friction force remains zero.
• The friction force increases and is in the same direction as your push.

Once the crate is sliding, how hard do you push to keep it moving at constant velocity?

• You push with a force slightly greater than the dynamic friction force.
• You push with a force equal to and opposite the dynamic friction force.
• You push with a force slightly greater than the static friction force.
• You no longer need to push once the crate is sliding.

Which is normally greater: static friction or sliding friction on the same object?

• Dynamic friction is normally greater than static friction.
• Static friction is normally greater than dynamic friction.
• On the same object, static friction and dynamic friction are equal.
• Static friction and dynamic friction are both zero.

How does the force of friction for a sliding object vary with speed?

• The force of friction is approximately independent of speed.
• The force of friction is proportional to speed.
• The force of friction is zero for a sliding object.
• The force of friction is inversely proportional to speed.

Does fluid friction vary with speed?

• Fluid friction is zero when an object moves.
• Fluid friction does not depend on speed.
• Fluid friction increases as speed increases.
• Fluid friction decreases as speed increases.