Midterm II: Study Module (Newton's Third Law and Applications)

You are lying on your back on the slope of a grassy hill, watching the clouds go by overhead. Which is the best statement about the force of friction exerted on you by the ground in this situation?

A force of static friction pointing "up the hill", parallel to the surface of the hill, is applied to you by the ground.

Josh punches his open left hand with his right hand. Which statement is true about the forces his two hands exert on each other?

Josh's right hand and left hand exert equal and opposite forces on each other.

While sparring, Katie punches Arman in the shoulder. Which statement is true about the forces Katie and Arman exert on each other?

Katie exerts a force on Arman's shoulder and Arman exerts a force on Katie's hand.

Michael leans on a shopping cart, causing it to start moving. Which statement is true about the forces Michael and the cart exert on each other?

Michael and the cart exert equal and opposite forces on each other.

Miguel leans against a wall. Which statement is true about the forces Miguel and the wall exert on each other?

Miguel and the wall exert equal and opposite forces on each other.

Jack and Luis are pushing on opposite ends of a shopping cart. At the moment, the cart is staying at rest. We know that the forces each person exerts on the cart are equal in magnitude and opposite in direction. What is the reason this must be true?

Newton's second law tells us these two forces must be equal and opposite.

Allison shoves her brother Brody away from her, causing him to fall down. Which of the following is an action-reaction pair (from Newton's third law)?

The force from Allison on Brody and the force from Brody on Allison form an action-reaction pair.

Blocks A and B have equal masses and are connected by a rope that passes over a frictionless pulley, as shown. At this moment, the system is at rest. Compare the magnitudes of the force of tension exerted on block A and the force of tension exerted on block B.

The force of tension exerted on block A is equal in magnitude to the force of tension exerted on block B.

Blocks A and B have equal masses and are connected by a rope that passes over a frictionless pulley, as shown. At this moment, the system is in motion, with block B moving downward and A moving upward at a constant speed. Compare the magnitudes of the force of tension exerted on block A and the force of tension exerted on block B.

The force of tension exerted on block A is equal in magnitude to the force of tension exerted on block B.

Stephanie pulls on a rope that is attached to a large crate. She is pulling the crate along at a constant speed as it slides across rough carpet. How does the magnitude of the force of tension exerted on Stephanie compare to the magnitude of the force of tension exerted on the crate?

The force of tension exerted on the crate has the same magnitude as the force of tension exerted on Stephanie.

In the figure, a hand is pushing on block B to the right, causing both blocks to move to the right across a rough surface at a constant speed. Compare the force that pushes block B to the right to the force that pushes block A to the right.

The force that pushes block A to the right is smaller than the force that pushes block B to the right.

Blocks A and B are connected by rope 1 and are pulled across a rough surface by rope 2, which is attached to block B, as shown. The applied force is strong enough to make the blocks speed up. Compare the magnitude of the tensions in ropes 1 and 2.

The magnitude of the tensions in the two ropes will not be equal.

Blocks A and B are connected by rope 1 and are pulled at constant speed across a rough surface by rope 2, which is attached to block B, as shown. Compare the magnitude of the tensions in ropes 1 and 2.

The magnitude of the tensions in the two ropes will not be equal.

You are standing in an elevator as it starts to move downward, accelerating for a moment. Which of these is true at that moment?

The net force on you changes from zero to downward as the elevator begins accelerating.

Consider a car driving at a constant speed on a level road. Which of the following is an action-reaction pair (from Newton's third law)?

The normal force exerted on the car by the road and the downward force exerted on the road by the car.

Consider a car speeding up as it drives along a level road. Which of the following is an action-reaction pair (from Newton's third law)?

The normal force exerted on the car by the road and the downward force exerted on the road by the car.

Allison pulls her little brother, Brody, in a sled on a snow-covered path at a constant speed. Which of the following is an action-reaction pair (from Newton's third law)?

The pulling force that Allison exerts on the sled and the pulling force that the sled exerts on Allison.

You are about to check out at the grocery store and you put a box of cereal on the conveyer belt at the register. The cashier turns on the conveyor belt, causing the box of cereal to speed up momentarily. At this moment, what can we say about the frictional force acting on the box of cereal?

There is a static frictional force pointing in the box's direction of motion, parallel to the conveyer belt.

Floating in deep space, you find yourself at rest next to a large asteroid. You reach out and tap the asteroid with a hammer. What happens to you in this process?

You will briefly accelerate away from the asteroid and then drift away at a constant speed.

In general, when a car is driving along a straight road, the force of friction between a car tire and the road _____________.

can point either forward or backward, depending on what the car is doing.

A person is trying to pull a heavy crate across a room with a rope that is attached to the crate, but it doesn't move. The tension in the rope ________________.

is equal at both ends of the rope

The mass of an object ______.

is not a vector and has no direction.

Consider a car at rest, parked on level ground. The force of friction between a car tire and the ground _____________________.

is zero

An object's mass and weight are _____.

proportional to each other.

A box rests on a table. The normal force exerted by the table on the box is equal in magnitude to the weight of the box and points in the opposite direction. This is because ________________.

the net force on the box is zero and, therefore, the forces must be balanced