Physics Ch 8-9

The unit of work is the

joule

This type of energy quadruples when the object's speed doubles

kinetic energy

A table tennis ball launcher is fired. Compared to the impulse on the ball, the impulse on the launcher is

the same

Sue can easily lift a 45.0-N rock with the help of a lever. When she pushes down with 20.0 N of force, she lifts the rock 0.3 meters. What is the mechanical advantage of the lever?

2.25

A person pushes on a 20 kg crate with 300 N of force. It doesn't move. How much work is done on the crate?

0

A lever has a theoretical mechanical advantage of 20. However, due to frictional forces the actual mechanical advantage is only 15. What is the efficiency of the lever?

0.75 (or 75%)

A woman can lift barrels a vertical distance of 1 meter or can roll them up a 2-meter long ramp to the same elevation. If she uses the ramp, the applied force required is

1/2 as much

How much power is expended if you lift a 40 N crate 5 meters in 2 seconds?

100 W

A pulley has two supporting strands. In order for it to lift a load 1 meter, the person wil have to pull a distance of

2 meters

A 6 kg object moves at 3 m/s. Its kinetic energy is

27 J

A freight car (mass 1000 kg) moves at a speed of 10 m/s. It runs into an identical car (mass 1000 kg) at rest on the track. The cars couple together. What is the velocity of the combined cars after the collision?

5 m/s

A 5-kg ball is thrown at 10 m/s. What is the ball's momentum?

50 kgm/s

If the car increases its speed from 20 km/h to 60 km/h, how many times more kinetic energy does it have?

9

An object at rest may have A energy B speed C velocity D momentum E none of the above

A

The amount of potential energy possessed by an elevated object is equal to A the work done in lifting it B the distance it is lifted C the force needed to lift it D the power to lift it

A

Which of the following is a vector? A momentum B work C kinetic energy D power E potential energy

A

A table tennis ball launcher is fired. Compared to the force on the ball, the force on the launcher is A larger B the same C smaller

B

Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a higher A acceleration B momentum C speed D all of the above E none of the above

B

When you jump off a step, you usually bend your knees as you reach the ground. Suppose the time impact is about 5 times more what it would be in a stiff-legged landing, then the average force on your body is reduced by A less than 5 times B about 5times C more than 5 times

B

A bug hits a windshield. Which of the statements is true? A The force on the bug is greater than the force on the windshield. B The impulse on the bug is greater than the impulse on the windshield. C The change in momentum of the bug is equal to the change in momentum of the windshield. D the change in velocity of the windshield is greater than the change in velocity of the bug E all of the above

C

As a pendulum swings back and forth A at the end points of its swing, its energy is all kinetic B at the lowest part of its swing, its energy is all potential C in between the highest and lowest points, it has both potential and kinetic energy D at the highest point, it is moving the fastest

C

If the velocity of a moving object doubles, then what else doubles? A acceleration B kinetic energy C momentum

C

Mechanical energy can be in the form of A kinetic energy B potential energy C both kinetic and potential D neither kinetic nor potential energy

C

Suppose a girl is standing on a pond where there is no friction between her feet and the ice. In order to get off safely she can A throw a ball upwards B throw a ball in the same direction she needs to travel C throw a ball in the opposite direction she needs to travel D throw a ball downward E walk on tiptoe

C

A pulley system can A change the direction of a force B multiply the force C increase the amount of work done D both A and B E Both B and C

D

Which of the following has the greatest momentum A a large truck parked in a parking lot B a tightrope walker crossing niagara falls C the science building at your school D a pickup truck traveling along the highway E a dog running down the street

D

Conservation of momentum states

In the absence of external forces, the momentum of a system is conserved.

A piece of putty and a rubber ball have the same mass. If you drop them from the same height, which object will produce a greater change in momentum and why?

The rubber ball will produce a greater change in momentum because it will bounce

In this type of collision, energy is turned into heat when objects get tangled together

completely inelastic

This type of potential energy is stored in a spring or rubber band

elastic

A popular toy consists of an aligned row of identical elastic balls suspended by strings so they touch each other. When two balls on one end are elevated and released, they slam into the array of balls and two balls pop out the other side. If instead, one ball popped out with twice the speed, this would be a violation of the conservation of

energy

How much farther will a car traveling at 100 km/s skid than the same car traveling at 50 km/s?

four times as far

If Nellie Newton pushes an object with twice the force for twice the distance, she does

four times the work

A force that always does negative work

friction

This depends on how high an object is with respect to a reference point

gravitational potential energy

This causes (and is equal to) change in momentum

impulse

When a car's speed triples, its kinetic energy

increases by nine times

Potential energy is the energy an object has because of its

location

The momentum of an object is defined as the object's

mass times its velocity

The ratio of output force to input force if a simple machine is called the

mechanical advantage

An object that has kinetic energy must have

momentum

Inertia in motion

momentum

A small economy car (low mass) and a lomousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. The car that has the most work done is

neither one - they receive the same amount of work done

A meteor that originally was heading East breaks up into two chunks. One of the chunks moves SouthEast. The second chunk was not immediately found, but scientists guessed that they should look for an object heading

northeast

The rate at which work is done or energy is transferred

power

This changes direction and/or multiplies force

simple machine

Which has greater kinetic energy, a car traveling at 30 km/h or a half-as-massive car traveling at 60 km/h?

the 60 km/h car

If you lift a load up two stories, how much work do you do compared to lifting one load up only one story?

twice as much

When a force is applied over a certain distance, ____ is done

work

Two gliders having the same mass and speed move toward each other on an air track and stick together. After the collision, the velocity of the gliders is

zero