Newtons 3rd law

Newtons Third law

A bicycle smashes into a concrete retaining wall. Describe how the force of the wall on the bicycle compares to the force of the bicycle on the wall

Equal and opposite

"The Rock" (150 kg) and Mini-Me (25 kg) collide at equal speeds. Who recoils (bounces back) faster?

Mini-Me because he has less mass

If you hit a closed steel door with a force of 48.5 N, how much force is exerted on you by the door?

-48.5 N

A single interaction involves \__ force(s)

2, action and reaction

As a prospective wrestler, you're afraid you won't make the weight when you need to. What is the best way to decrease the reading on the scale without changing your body's mass?

Push down on or lean against something nearby

When a horse pulls a wagon, what is the force that causes the horse to move forward?

The ground pushing against the horse's hooves

A player catches a ball. Consider the action force to be the impact of the ball against the player's glove. What is the reaction to this force?

The glove against the ball

A player hits a ball with a bat. The action force is the impact of the bat against the ball. What is the reaction to this force?

Ball against the bat

A baseball player bats a ball with a force of 1000 N. The ball exerts a reaction force against the bat of (how large?)

-1000 N

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

the cat pulling back up on the earth

A Mack truck and a Volkswagen traveling at the same speed collide head-on. Compare their impact forces.

Impact forces are the same size, but the VW has less mass so it is affected more by the collision

A Mack truck and a Volkswagen traveling at the same speed collide head-on. Which vehicle will undergo the greatest change in velocity ?

The VW experiences the greatest change in velocity because of its smaller mass.

The amount of attraction between an object on or near Earth's surface and the Earth is called

weight

The relationship between mass (m) and weight (w) is given by the equation

w \= mg__weight \= mass x (acceleration due to gravity

A mass is accelerated when an \_____ acts upon the mass.

unbalanced force ("net force")

Rockets are unable to accelerate in space because

nonsense! Rockets can accelerate in space. Rocket pushes out the gas, so the gas pushes back on the rocket and propels it..

A gun recoils when it is fired. The recoil ("kick") is the result of action-reaction force pairs. The gun pushes the bullet forward and the bullet pushes the gun backward. Compare the accelerations of the recoiling gun and the bullet.

The bullet accelerates more because it has less mass.

In the top picture, a physics student is pulling upon a rope that is attached to a wall. In the bottom picture, the physics student is pulling upon a rope that is held by the Strongman. In each case, the force scale reads 500 Newtons. In which case is the physics student is pulling with more force?

Student pulls with the same amount of force in both cases because the scale reads the same for both.

Forces always occur . . . alone? In pairs? In triplets?

In pairs

According to Newton's third law, if you push gently on something, it will push ...

gently back on you

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

road

. Three books, X, Y, and Z, rest on a table as shown in the diagram below. The weight of each book is indicated. How large is the net (unbalanced) force acting on book Y?

ZERO because Book Y is not changing its motion.

Whenever a force is exerted, another force occurs that is \____ in size, and \_____ in direction.

equal, opposite

. Is the force exerted on the racket by a hit tennis ball the action, the reaction, or can you tell?

Cannot tell and it's not important

An object's momentum is determined by the object's \______ and \_____________.

mass, velocity

What is the momentum of a 0.255-kg apple when it is rolling at 16.0 m/s?

p \= mvp \= (0.255)*(16.0)p \= 4.08 kg m/s

. Choose the object that has a momentum of zero.

Choose the object that is not moving.

Calculate the velocity of a 90.5 kg man running south with a momentum of 389 kg m/s.

p \= mv389 \= (90.5)v

If you divide momentum by velocity, the result is the value of the object's

mass

A 10.0 kg dog chasing a rabbit north at 6.0 m/s has a momentum of ...

60 kg m/s north

. If the net force on an object is zero then the object has \_________ forces.

no unbalanced

. Choose the object does not have momentum?

Again, choose the one that's not moving

The greatest change in momentum will be produced by a \______ force acting during a \____ time.

large, long

. A 10-kg rock has a velocity of 20 m/s. If a ball with a velocity of 50 m/s has the same momentum as the rock, the mass of the ball is \_____.

P of rock \= p of ball(10 kg)*(20 m/s) \= m*(50 m/s)

200 \= 50m

200/50 \= m

4 \= m

Impulse can be represented by which symbols?

Force x change in time \= F*Dt

When a golfer hits a golf ball, the force exerted by the ball on the club is \_____ the force exerted by the club on the ball.

equal and opposite from

A Ping-Pong ball gun is fired. The amount of impulse on the gun is the\_____ compared to the impulse on the gun.

same as

Momentum can be calculated by multiplying \_____.

mass times velocity

If no net force acts on a body, how is its motion affected?

Motion is not affected.

Which has more momentum: a large truck moving at 30 miles per hour, or a small truck moving at 30 miles per hour?

Large truck because it has more mass

A sports car is moving at 60 miles per hour when it enters a construction zone. The car then quickly (safely!) slows to 30 miles per hour. How does its momentum through the construction zone compare to its momentum before the zone?

Momentum before the zone is twice as much as it is during the zone

If the momentum of an object changes, and its mass remains constant, then what can you tell about its velocity, acceleration, and any forces acting on it?

Velocity changes; acceleration occurs; a net force is acting on it

According to the impulse-momentum theorem, the change in momentum of an object is equal to the

impulse acting on the object

If Superman at rest in free space throws an asteroid that has more mass than Superman, then which moves away faster?

Superman because he has less mass

Skelly the skater is traveling at high speed, so he needs a certain amount of force to stop him. How would this force have to change if he (a) has more mass? (b) has more momentum?

(c) has less stopping distance? (d) undergoes all of these changes? (a) increase the force; (b) increase the force; (c) increase the force; (d) REALLY increase the force

A well-hit golf ball has a momentum of 5 kg m/s. If the impact lasts 0.1 s, what is the average force exerted on the ball by the club?

F*change in time \= mass *change in momentum

F* (0.1 s) \= 5 kg m/s

F\= 50 N

Auto companies frequently test the safety of automobiles by putting them through crash tests to observe the integrity of the passenger compartment. If a 1000-kg car is sent toward a cement wall with a speed of 14 m/s and the impact brings it to a stop in 0.08 s, with what average force is it brought to rest?

F* change in time \= mass * change in velocity

Change in velocity \= -14 m/s

F (0.08) \= (1000)(-14 m/s)

F \= -175,000 N

Why does a gun kick when fired?

Because the bullet pushes back against it.

Airbags can save lives because . . .

increase the collision time