Mid-Term Prep: Unit 2

Front

Which law best explains why the coin sitting on top of the ring falls directly into the jar?

Back

Newton's 1st Law - Inertia

Answer explanation

Inertia - means a resistance to a change in velocity. The inertia of the coin tries to keep the coin from moving to the right.

Front

A northbound car makes a sharp right turn to go east. As the car turns, the groceries in the back seat slide to the left side of the car. What causes the groceries to slide to the left?

Back

Inertia

Answer explanation

Newton's 1st Law - Law of Inertia

All objects resist changes in velocity

• - resist a change in speed

• - resist a change in direction

The inertia of the groceries makes them want to continue to move in the same direction (north) even as the car turns to the east.

Front

If we apply a ___________ to an object, its __________________ will change and it will  ______________ in the same direction as the net force.

Back

net force, velocity, accelerate

Front

A 10N force is applied to a mass as it moves to the right on a frictionless surface. If the mass is tripled, what happens to the acceleration?

Back

It is 1/3 as large.

Answer explanation

Acceleration is inversely proportional to mass. Thus, if you triple the mass, the acceleration is cut to 1/3 of its original value.

Acceleration is directly proportional to force. Thus, if you triple the force, the acceleration will triple.

Front

How much force is required to keep a 4-kg object moving to the right with a constant speed of 8.0 m/s on a frictionless surface?

Back

0 N

Answer explanation

To maintain a constant speed on a frictionless surface, no net force is required.

Front

F_g is always directed

Back

toward the center of the planet

Front

Force Gravity and Force Normal are an action-reaction pair (force pair)?

Back

False

Answer explanation

While Force Gravity and Force Normal can sometimes appear to be action-reaction pair, they are not. In order to be an action-reaction pairs, the forces should be of equal magnitude and point in opposite directions.

Inclines are common example that demonstrates Force Gravity and Force Normal are not an action-reaction pair. On an incline, Force Gravity points toward the center of the planet while Force Normal points perpendicular to the surface.

Front

A small, positively-charged ball is suspended in equilibrium from a vertical wall by a thread. What is the net force acting on the ball?

Back

Zero

Answer explanation

If an object is in equilibrium, then the acceleration and Net Force are both zero

Front

Which FBD diagram shows an elevator moving downward and slowing down? A, B, C, none of these

Back

B

Answer explanation

Since the movement is downward the velocity points downward. In order to "slow down" velocity and acceleration must point in opposite directions. Thus, acceleration must be upward.

If acceleration is upward, then the Net Force is upward. This is consistent with diagram B.

Front

An object is hanging at the end of a rope and accelerates upwards at a rate of 3.0 m/s². Which statement regarding the tension in the rope is true?
The tension in the rope is equal to the weight of the object.
The tension in the rope is more than the weight of the object.
The tension in the rope is less than the weight of the object.
Any of the above statements could be true based on the mass of the object.

Back

The tension in the rope is more than the weight of the object.

Answer explanation

The object accelerates upwards at 3.0 m/s², indicating that the net force is upward. Therefore, the tension must be greater than the weight to provide this upward acceleration.