Physics Chapter 8

When the force of impact on an object is extended in time, does the impulse increase or decrease?

Increases

Is the following sentence true or false? If a system undergoes changes wherein all the forces are internal, such as an atomic nuclei undergoing nuclear decay, the net momentum of the system before and after the event is the same.

True

The force on the cannonball inside the cannon barrel is equal_______

by something outside the object.

If you wish to change the momentum of an object________

exert an impulse on it.

What is the quantity force x time interval?

impulse

Is momentum a vector or a scalar quantity?

vector

Circle the letter of each sentence that is true. a. The vector sum of the momenta is the same before and after a collision. b. The momentum of the car wreck is not equal to the vector sum of the momenta of car A and car B before the collision. c. When a firecracker bursts, the vector sum of the momenta of its fragments add up to the firecracker's momentum just before bursting. d. Momentum is not conserved for high-speed elementary particles in bubble chambers.

A C

What factors affect an object's momentum?

A moving object can have a large momentum if it has a large mass, a high speed, or both

Explain why the total momentum of a cannon-cannonball system is zero after firing.

After firing, the net momentum, or total momentum, is zero because the momentum of the cannon is equal and opposite to the momentum of the cannonball.

Circle the letter of each sentence that is true about impulse and momentum. a. When jumping from an elevated position down to the ground, you should keep your legs stiff to decrease the momentum. b. A wrestler thrown to the floor should extend his time hitting the mat by relaxing his muscles and spreading the impulse to his foot, knee, hip, ribs, and shoulder. c. When a boxer gets punched, she should move her head away from the punch to increase the contact time and reduce the force. d. A dropped dish is more likely to survive a fall on carpet rather than concrete, because the softness of the carpet leads to increased contact time.

B C D

Does impulse equal momentum, or a change in momentum?

Change in momentum

What is the difference between an elastic collision and an inelastic collision?

Elastic Collision- when objects collide without being permanently deformed and without generating heat Inelastic Collision- a collision in which the colliding objects become distorted and generate heat during the collision

What is the formula that relates impulse and change in momentum?

F/\t = /\(mv)

Is the following sentence true or false? The impulse required to bring an object to a stop and then to "throw it back again" is less than the impulse merely to bring the object to a stop.

False

Is the following sentence true or false? Whenever objects collide in the absence of external forces, the net momentum of both objects before the collision does not equal the net momentum of both objects after the collision.

False

The change in momentum depends on the _________ and the length of _________ it acts.

Force Time

Distinguish between force and impulse.

Force is a push or pull Impulse = force x time.

In a car crash, why is it advantageous for an occupant to extend the time during which the collision takes place?

Greater time means less force.

Why is it advantageous for a boxer to ride with the punch? Why should he avoid moving into an oncoming punch?

Greater time means less force; less time means greater force.

What is the main point of the law of conservation of mass?

It describes the momentum of a system.

If the time of impact in a collision is extended by four times, how much does the force of impact change?

It is reduced to one fourth.

A moving object can have a large momentum if it has _____________ a _____________ or both.

Large Mass High Speed

What is the difference between mass and momentum?

Mass is inertia Momentum is inertia in motion.

The mass of an object multiplied by its velocity

Momentum

Describe how the velocities of each of the billiard balls changes in the elastic collisions always.

The balls will always exchange velocities

Explain why a baseball player follows through with his or her swing.

The baseball player wants to apply the greatest force possible for as long as possible so that the ball goes as far as possible.

In terms of momentum conservation, why does a cannon recoil when fired?

The cannon's momentum must be equal and opposite to that of the cannonball.

What factors affect how much an object's momentum changes?

The change in momentum depends on the force that acts and the length of time it acts.

Why is more impulse delivered during a collision when bouncing occurs than during one when it doesn't?

The change in momentum is greater so the impulse is greater.

What 2 things does the change in momentum depend on?

The force that acts and the length of time it acts.

How does the impulse of a bounce compare to stopping only?

The impulse required to bring an object to a stop and then to "throw it back again" is greater than the impulse required merely to bring the object to a stop.

What does the law of conservation of momentum state?

The law of conservation of momentum states that, in the absence of an external force, the momentum of a system remains unchanged.

What does it mean to say that momentum is conserved?

The momentum before the collision is the same as the momentum after the collision.

Whenever objects collide in the absence of external forces, _______

The net momentum of both objects before collision equals the net momentum of both objects after collision.

Which has the greater mass, a heavy truck at rest or a rolling skateboard? Which has greater momentum?

The truck The rolling skateboard

What is true about the vector sum of momenta in a collision?

The vector sum of the momenta is the same before and after a collision

If a force is increased on an object, what happens to the velocity and the momentum?

There is a greater change in velocity and momentum.

Is the following sentence true or false? By hitting a soft object, such as a haystack, instead of a hard object, such as a concrete wall, you extend the contact time in which the momentum is brought to zero.

True

Is the following sentence true or false? If the momentum of an object changes, either the mass or the velocity or both change.

True

Is the following sentence true or false? The law of conservation of momentum states that, in the absence of an external force, the momentum of a system remains unchanged.

True

How does conservation of momentum apply to collisions?

Whenever objects collide in the absence of external forces, the net momentum of both objects before the collision equals the net momentum of both objects after the collision.

Is momentum conserved for colliding objects that are moving at angles to one another? Explain.

Yes. Resulting motions follow the vector rules.

The force or impulse must be exerted on the object ________

by something outside the object.

What two conservation laws are the most powerful tools in the study of mechanics?

conservation of momentum and conservation of energy

When objects collide without being permanently deformed and without generating heat, the collision is said to be a(n) _______

elastic collision

Is this sentence true or false? Momentum is conserved only when interacting objects move along the same straight path.

false

Distinguish between impact and impulse. Which designates a force and which is force multiplied by time?

impact designates a force; impulse = force x time.

What is the short-hand notation for impulse?

impulse = F/\t

Distinguish between impulse and momentum. Which is force x time and which is inertia in motion?

impulse = force x time; momentum is inertia in motion.

A collision in which the colliding objects become distorted and generate heat during the collision is a(n)________

inelastic collision

What is the equation for momentum?

momentum = mass × velocity = mv

If no outside force is present ________

no change in momentum is possible.