Physics Chapter 8

P=W/t W=Fd P=(30 X 5)/8 = 18.75 There is gravity involved so 18.75(10) 187.5 W

A 30-kg girl runs up the staircase to a floor 5 m higher in 8 seconds. What is her power output?

c. less than 100 J

A ball is thrown into the air with 100 J of kinetic energy, which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is a. 100 J. b. more than 100 J. c. less than 100 J.

b. 75.0 N

A frictionless inclined plane is 8.0 m long and rests on a wall that is 2.0 m high. How much force is needed to push a block of ice weighing 300.0 N up the plane? a. 37.5 N b. 75.0 N c. 100.0N d. 300.0 N e. 600.0 N

a. 10%

A machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is a. 10%. b. 50%. c. 90%. d. 110%. e. none of the above

d. Both A and B

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

False

A pulley system can change only direction; it can't multiple forces as well

c. neither A nor B (same for each).

A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. The car that receives the greater impulse is the a. limousine. b. small economy car. c. neither A nor B (same for each).

b. 1/2 as much

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 a. 1/4 as much. b. 1/2 as much. c. the same amount. d. 2 times as much. e. 4 times as much.

d. work input equals work output

All simple machines ideally work on the principle that a. impulse equals momentum change. b. force equals mass times acceleration. c. total momentum before a collision equals total momentum after the collision. d. work input equals work output. e. kinetic energy transforms into potential energy.

d. 70 J

An arrow in a bow has 70 J of potential energy. Assuming no loss of energy to heat, how much kinetic energy will it have after it has been shot? a. 0 J b. 35 J c. 50 J d. 70 J e. 140 J

a. energy

An object at rest may have a. energy. b. speed. c. velocity. d. momentum. e. none of the above

e. all of the above

As a pendulum swings back and forth a. at the end points of its swing, its energy is all potential. b. at the lowest part of its swing, its energy is all kinetic. c. kinetic energy is transformed into potential energy. d. potential energy is transformed into kinetic energy. e. all of the above

e. 75 J

How many joules of work are done on a box when a force of 25 N pushes it 3 m? a. 1 J b. 3 J c. 8 J d. 25 J e. 75 J

e. 600 W

How much power is expended if you lift a 60 N crate 10 meters in 1 second? a. 0 W b. 6 W c. 10 W d. 60 W e. 600 W

c. 8 W

How much power is required to do 40 J of work on an object in 5 seconds? a. 0 W b. 5 W c. 8 W d. 40 W e. 200 W

e. 40 J

How much work is done on a 20-N crate that you lift 2 m? a. 0 J b. 1 J c. 2 J d. 20 J e. 40 J

a. 0 J

How much work is done on a 60-N box of books that you carry horizontally across a 6-m room? a. 0 J b. 6 J c. 10 J d. 60 J e. 360 J

c. momentum

If an object has kinetic energy, then it also has...

dependent on the mass of the barbell

If possible, determine the power expended when a barbell is raised 5.0 m in 2 s.

d. twice

If you lift two loads up one story, how much work do you do compared to lifting just one load up one story? a. One quarter as much b. One half as much c. The same amount d. Twice as much e. Four times as much

False

In physics the amount of work done on an object is the product of the force exerted on the objects times the time the object moves (TRUE OR FALSE)

e. force times distance

In physics, work is defined as a. force times time. b. force divided by distance. c. distance divided by time. d. force divided by time. e. force times distance.

b. 10 N

It takes 80 J to push a large box 8 m across a floor. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box? a. 8 N b. 10 N c. 80 N d. 640 N e. none of the above

b. one half the product of its mass times its speed squared

Kinetic energy of an object is equal to a. its mass multiplied by its acceleration squared. b. one half the product of its mass times its speed squared. c. its mass multiplied by its speed. d. one half the product of its mass times its speed. e. its mass multiplied by its acceleration.

False

More power is needed to carry a heavy suitcase slowly up a flight of stairs than to carry the suitcase quickly up the same flight of stairs

c. Position

Potential energy is the energy an object has because of its a. density b. size c. position d. speed e. temperature

c. work done on an object divided by the time taken to do the work

Power is defined as the a. force on an object divided by the time the force acts. b. work done times the time taken to do that work. c. work done on an object divided by the time taken to do the work. d. distance divided by the time taken to move that distance. e. force on an object times the distance the object moves.

d. the work done in lifting it

The amount of potential energy possessed by an elevated object is equal to a. the power used to lift it. b. the distance it is lifted. c. the force needed to lift it. d. the work done in lifting it. e. the value of the acceleration due to gravity.

e. mechanical advantage

The ratio of output force to input force of a simple machine is called the a. fulcrum. b. efficiency. c. pivot point. d. lever arm. e. mechanical advantage.

E efficiency

The ratio of useful work output to total work input is called the a. mechanical advantage. b. lever arm. c. pivot point. d. fulcrum. e. efficiency.

e. watt

The unit of power is the a. newton. b. meter. c. joule. d. second. e. watt.

c. joule

The unit of work is the a. watt. b. meter. c. joule. d. newton. e. second.

W= 30(9) (NO GRAVITY INVOLVED) 270 J

What amount of work is done on a chair that is pushed 9 m across a floor by a horizontal 30-N net force?

Power

What is the rate at which work is done?

W= Fd W= 60(20)= 120 There is gravity involved so 120(10) 12,000 J

What is the work done in lifting 60 kg of blocks to a height of 20 m?

W= 20(5)= 100 There is gravity involved so 100(10) 1000 J

What is the work done in raising a 20-kg block 5 m vertically?

d. increases by nine times

When a car's speed triples, its kinetic energy a. remains the same. b. triples. c. increases by four times. d. increases by nine times. e. none of the above

True

When we carry an object across the room, without lifting it or setting it down we do no physical work on it

a. the 60 km/h car

Which has greater kinetic energy, a car traveling at 30 km/h or a half-as-massive car traveling at 60 km/h? a. The 60 km/h car b. Both have the same kinetic energy. c. The 30 km/h car

c. both require the same amount of work

Which requires more work: lifting a 70-kg sack vertically 2 meters or lifting a 35-kg sack vertically 4 meters? a. Lifting the 70 kg sack b. Lifting the 35 kg sack c. Both require the same amount of work.

b. energy

a popular toy consists of an aligned row of identical elastic balls suspended by strings so they also 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 a. both energy and momentum b. energy c. momentum