P199 Homework 2

A 10-N falling object encounters 10 N of air resistance. The net force on it is

0 N.

A hockey puck slides across a frozen pond. If ice friction and air resistance are neglected, the force needed to keep the puck sliding at constant velocity is

0 N.

A rock is thrown vertically upward. At the top of its straight-line path, its velocity is

0 m/s.

A sack of potatoes weighing 200 N falls from an airplane. As the velocity of fall increases, air resistance also increases. When air resistance equals 200 N, the sack's acceleration is

0 m/s^2.

A 10-kg block is pushed across a horizontal surface with a horizontal force of 20 N against a friction force of 10 N. The acceleration of the block is

1 m/s^2.

A 1-kg ball is thrown straight up at 10 m/s. Neglecting air resistance, the net force that acts on the ball when it is half way to the top of its path is

10 N.

A 10-kg brick and a 1-kg book are dropped in a vacuum. The force of gravity on the 10-kg brick is

10 times as much as the force on the 1-kg book.

A 10-N block and a 1-N block lie on a horizontal frictionless table. To push them with equal acceleration, we would have to push with

10 times as much force on the heavier block.

A push on a 1-kg brick accelerates the brick. Neglecting friction, to equally accelerate a 10-kg brick requires the force to be

10 times as much.

When a baseball player hits a ball with a force of 1000 N, the ball exerts force on the bat of

1000 N.

A tow truck exerts a force of 3000 N on a car that accelerates at 2 m/s^2. The mass of the car must be

1500 kg.

A 10-kg block is pushed across a friction-free horizontal surface with a horizontal force of 20 N. The acceleration of the block is

2 m/s^2.

A 10-kg block is pushed across a horizontal surface with a horizontal force of 30 N against a friction force of 10 N. The acceleration of the block is

2 m/s^2.

A commercial jet has a mass of 5,000 kg and the thrust of its engine is 10,000 N. The acceleration of the jet when taking off is

2 m/s^2.

A jumbo jet has a mass of 100,000 kg. The thrust for each of its four engines is 50,000 N. The acceleration of the jet when taking off is

2 m/s^2.

A car has a mass of 1000 kg and accelerates at 2 m/s^2. What is the magnitude of the force exerted on the car?

2000 N

A girl pulls on a 10-kg wagon with a constant force of 30 N. What is the wagon's acceleration?

3.0 m/s^2.

When a 500-N parachutist opens his chute and experiences 800 N of air resistance, the net force on him is

300 N upward.

A karate chop breaks a board with a blow of 3000 N. The force that acts on the hand during this event is

3000 N.

Two people, one twice as massive as the other, attempt a tug-of-war with 12 m of rope on frictionless ice. After a brief time, they meet. The heavier person slides a distance of

4 m.

Both ends of a piece of rope are pulled by two people in a tug-of-war. If each pulls with a 400-N force, the tension in the rope is

400 N.

A person is attracted toward the center of Earth by a 500-N gravitational force. The force of attraction of Earth toward the person is

500 N.

A skydiver who weighs 500 N reaches terminal velocity at 90 km/h. The air resistance on the skydiver is

500 N.

A 10-N falling object encounters 4 N of air resistance. The net force on it is

6 N.

A block is dragged at constant velocity across a level surface by a force of 6 N. What is the force of friction between the block and the surface?

6 N.

A Honda Civic Hybrid weighs about 3050 lb . A. Calculate the weight of the car in newtons. (Note: 0.22 lb =1N). B. Calculate the mass of the car in kilograms. (Note: 1 kg on Earth's surface has a weight of 10 N).

A. W = 1.4×104 N B. m = 1400 kg

A business jet of mass 32000 kg takes off when the thrust for each of two engines is 28000 N . A. Find its acceleration.

A. a = 1.8 m/s^2

The auto in the sketch moves forward as the brakes are applied. A bystander says that during the interval of braking, the auto's velocity and acceleration are in opposite directions. Do you agree or disagree?

Agree. Acceleration (slowing the car) is opposite to velocity (the direction the car is moving).

Earth pulls on the Moon. Similarly the Moon pulls on Earth, evidence that

Earth and Moon pull on each other. Earth's and Moon's pulls comprise an action-reaction pair.

A rocket of mass 90000 kg undergoes an acceleration of 3.0 m/s2 . A. Find the net force acting on it.

Fnet = 2.7×105 N

A simple rearrangement of Newton's second law gives Fnet=ma. Find a net force that is needed to give a 15-kg package an acceleration of 6.2 m/s2 . (Note: The units kg⋅m/s2 and N are equivalent.).

Fnet = 93 N

A Mack truck and a Mini Cooper traveling at the same speed collide head-on. The vehicle to undergo the greatest change in velocity will be the

Mini Cooper

Arnold Strongman and Suzie Small have a tug-of-war on a polished floor. Arnold wears socks and Suzie wears gym shoes. The likely winner is

Suzie.

In the textbook acceleration is defined as a=Δv/Δt. Use this formula to find the acceleration of a cart on an inclined plane that gains 6.6 m/s each 1.4 s .

a = 4.7 m/s^2

Action and reaction forces comprise the parts of

a single interaction.

If gravity between the Sun and Earth suddenly vanished, Earth would continue moving in

a straight-line path.

When you step off a bus moving at 10 m/s, your horizontal speed when you meet the ground is

about 10 m/s.

If the mass of an object does not change, a constant net force on the object produces constant

acceleration.

Newton's second law directly involves

acceleration.

A falling object that has reached its terminal speed continues to gain

acceleration. speed. **neither**

A friend says that the heavyweight champion of the world cannot exert a force of 50 N on a piece of tissue paper with his best punch. The tissue paper is held in midair, no wall, no tricks. You...

agree that it can't be done.

Earth moves about 30 km/s relative to the Sun. When you jump upward in front of a wall, the wall doesn't slam into you at 30 km/s because the wall

and you move at the same horizontal speed, before, during, and after your jump.

An archer shoots an arrow. If the action force is the bowstring on the arrow, the reaction is the

arrow's push on the bowstring.

A heavy object and a light object in a vacuum are dropped at the same time from rest. The heavier object reaches the ground

at the same time as the lighter object.

A player hits a ball with a bat. If one part of the interaction is the bat against the ball, the other part is the

ball against the bat.

A given net force propels an object along a straight-line path by a force. If the mass were doubled, its acceleration would

be half.

If an object falls with constant acceleration, the velocity of the object must

continually change by the same amount each second.

Suppose you're coasting in a car at 60 km/h and apply the brakes until you slow to 40 km/h. When you suddenly release the brake, the car tends to

continue moving at 40 km/h in the absence of forces.

A skydiver jumps from a high-flying plane. As her velocity of fall increases, her acceleration

decreases.

When an object falls through the air and gains velocity, the net force actually

decreases.

A ball tossed vertically upward reaches its highest point and then falls back to its starting point. During this up-and-down motion the acceleration of the ball is always

directed downward.

A given net force propels an object along a straight-line path. If the net force were doubled, its acceleration would

double.

When you toss a coin straight up, it moves upward, turns around, and drops. During this time the acceleration of the coin is

downward and constant.

An elephant and a feather fall from a tree through the air to the ground below. The force of air resistance is greater on the

elephant.

A space probe in remote outer space continues moving

even though no force acts on it.

Inside the interior of a truck that moves at constant velocity is a package that drops from the midpoint of the ceiling. The package hits the floor

exactly below the midpoint of the ceiling.

Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the rock tends to

follow a straight-line path.

A player catches a ball. Consider the action force to the ball against the player's glove. The reaction is the

force of the glove on the ball.

Two objects of the same size but unequal weights are dropped from a tall tower. Taking air resistance into consideration, the object to hit the ground first will be the

heavier object.

A ball rests in the middle of a cart. When you quickly jerk the cart forward, the ball

hits the back of the cart.

A heavy block at rest is suspended by a vertical rope. When the block is accelerated upward by the rope, the rope tension

increases.

If an object's mass decreases while a constant force acts on it, the acceleration

increases.

If you are carrying a heavy bag of groceries and bang your hand against the wall, the concept that best explains why you are hurt is

inertia.

When dishes remain on a table when you yank the tablecloth beneath them, you're demonstrating

inertia.

You toss a ball upward where air resistance is negligible. After the ball leaves your hand the force on it

is the single force due to gravity, always directed downward.

A pair of tennis balls fall through the air from a tall building. One ball is regular and the other is filled with lead pellets. Air resistance just before they hit is actually greater for the

lead-filled ball.

A pair of tennis balls fall through the air from a tall building. One ball is regular and the other is filled with lead pellets. The ball to reach the ground first is the

lead-filled ball.

A ball is thrown vertically upward. Because of air resistance, its speed when returning to its starting level compared with its initial speed is

less.

How many forces act on an upwardly tossed coin when it gets to the top of its path?

one; the force due to gravity.

As a ball falls, the action force is the pull of Earth's mass on the ball. The reaction force is the

pull of the ball's mass on Earth.

After a ball tossed upward leaves your hand, the force of gravity on it

remains constant.

The force exerted on the tires of a car to directly accelerate it along a road is exerted by the

road.

A Mack truck and a Mini Cooper traveling at the same speed collide head-on. The collision force is greatest on the

same for both.

A car traveling at 100 km/h strikes an unfortunate bug that splatters on the windshield. The force of impact is greater on the

same for both.

Arnold Strongman and Suzie Small each pull on opposite ends of a rope in a tug-of-war. The greatest force on the rope is exerted by

same for both.

The air resistance of falling is greatly affected by an object's frontal area and

speed.

A sheet of paper can be pulled from beneath a box of cereal without toppling it if the paper is jerked quickly. This best demonstrates that

the box has inertia.

A light woman and a heavy man jump from an airplane at the same time and open their same-size parachutes at the same time. Which person will get to a state of zero acceleration first?

the light woman.

A roller coaster car at an amusement park carrying 1 passenger takes 3 min to make its ride from start to finish. Neglecting friction, a car with 5 passengers would take

the same time.

A force of 1 N accelerates a 1-kg mass at 1 m/s2. The acceleration of a 2-kg mass acted upon by a force of 2 N is

the same.

The force required to maintain an object at a constant velocity in free space is equal to

zero.

The net force on any object moving at constant velocity is

zero.

When a falling object has reached its terminal velocity, its acceleration is

zero.