Physics Ch. 9 Test review guide

a certain jack has a theoretical mechanical advantage of 500. However, due to frictional forces, the actual mechanical advantage is only 100. What is the efficiency of the jack?-500; 5; 50,000; 50; 1/5

1/5

a machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is _____. -10%; 90%; 110%; 50%

10%

a frictionless inclined plane is 6m long and rests on a wall that is 2m high. How much force is needed to push a block of ice weighing 300 N up the plan?-50 N; 300 N; 100 N; 200 N; 600 N

100 N

suppose a moving car has 3000 J of kinetic energy. if the car's speed doubles, how much kinetic energy will it then have?

12,000 J

a pulley has two supporting strands. In order to use it to lift a load 1 meter, the person pulling will have to pull a distance of _______.-1; 2; 1/4; 4; 1/2

2

how much power is expended if you lift a 50 N box 4m in 1 second?

200 W

how much work is done on a 60 N crate that you lift 6m?

360 j

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

4 x

how much power is required to do 10 J of work on an object in 2 seconds?

5 W

a 100 N object moves at 1 m/s. its kinetic energy is...

5 j

how many joules of work are done on an object when a force of 10 N pushes it 5m?-50; 10; 1; 2; 5

50

how much power is required to do 100 j of work on an object in 2 seconds>-0; 50; 2; 200; 100

50

it takes 30 J to push a large box 5m across a floor. assuming the push is in the same direction has the move, what is the magnitude of the force on the box?

6 N

an arrow in a bow has 70 J of potential energy. Assuming no loss of energy due to heat, how much kinetic energy will it have after it has been shot?-140 J; 0; 35; 70; 50

70

an arrow in a bow has 70 J of PE. assuming no loss of energy to heat, how much KE will it have after it has been shot?

70 j

how many joules of work are done on a crate when a force of 20 N pushes it 4m?

80 j

How will a lubricant affect the efficiency of a simple machine such as a pulley?

A lubricant will increase a simple machine's efficiency by decreasing friction, which increases work output.

T/F: a pulley system can only change direction; it can't multiply forces as well

False

T/F: the ratio of output force to input force for a simple machine is its efficiency

False

What are the details of a first class lever?

First class levers have the fulcrum (F) between the input (I) and the output (O) forces

Liz throws a softball with a force of 63 N a distance of 25 m. Jamie throws the softball with the same amount of force, but the ball only goes 17 m. Which girl does less work? a. They do the same amount of work b. Liz c. Jamie d. Neither girl does any work.

Jamie

The unit of work is the...?

Joule

If two swimmers compete in race, does the faster swimmer automatically develop more power?

Power depends on work and time, from which you can extrapolate that it depends on force and velocity. If the slower swimmer exerts more force (e.g. she is larger and has to use more force to propel herself), then she might develop more power

What are the details of a second class lever?

Second class levers apply the output (O) force between the fulcrum (F) and the input (I) force

What are the details of a third class lever?

Third class levers have the input (I) force applied between the fulcrum (F) and the output (O) force

T/F: The unit of power is the watt

True

T/F: The unit of work is called a joule

True

T/F: using an incline plane is an effective way to lift a heavy object that you couldn't otherwise lift

True

the unit of power is the _______.

Watt

a pulley system can ______.-change the direction of a force; multiply the force; increase the amount of work done; A and B

a and b

A mechanical device requires 420 J of work to do 230 J of work in lifting a crate. What is the efficiency of the device? a. 55% b. 183% c. 190% d. 0.5%

a. 55%

If you know the input distance and output distance of a machine, which of the following can you calculate? a. ideal mechanical advantage b. actual mechanical advantage c. efficiency d. work

a. ideal mechanical advantage

Which of the following statements indicates the best way to increase power? a. increase the amount of work done in a given amount of time, or do a given amount of work in less time b. increase the amount of work done in a given amount of time, or do a given amount of work in more time c. decrease the amount of work done in a given amount of time, or do a given amount of work in less time d. decrease the amount of work done in a given amount of time, or do a given amount of work in more time

a. increase the amount of work done in a given amount of time, or do a given amount of work in less time

Some simple machines are closely related to one another because of their shape or function. A variation of an inclined plane is a ________________________________. a. wedge b. wheel & axle c. lever d. pulley

a. wedge

If Antonia exerts a force of 700 N to walk 6 m up a flight of stairs in 6 s, how much power does she use? a. 25,200 W b. 700 W c. 19 W d. 4200 W

b. 700 W

When a machine does work, a trade-off occurs. Which of the following best exemplifies that trade-off? a. A ramp allows you to decrease force, but requires a greater input force. b. A pulley changes the direction of your force, but requires a greater input force. c. A lever increases output force and the distance the load moves. d. A wheel and axle decreases output force and the distance the load moves.

b. A pulley changes the direction of your force, but requires a greater input force.

Alex helps his teacher lift a 200-N box of books 1.2 m from the floor to the desktop. In which of the following situations will he do more work? a. He lifts a 98-N box to the same height. b. He lifts a box of the same weight 1.7 m. c. He lifts a box of the same weight 0.9 m. d. He lifts a 175-N box to the same height.

b. He lifts a box of the same weight 1.7 m

In which of the following scenarios is work being done, according to the scientific definition? a. Jose solves a "work" calculation in his head. b. Shasta lifts her chair onto the desk after the afternoon announcements. c. Garrett holds a barbell still over his head in weightlifting class. d. Paige carries a reference table across the classroom.

b. Shasta lifts her chair onto the desk after the afternoon announcements

The Law of Conservation of Energy explains that while work input is greater than work output for all machines, the "missing" energy must have been _________________________________________. a. miscalculated b. converted into something like friction c. converted back into input energy d. lost

b. converted into something like friction

An inclined plane reduces effort force by ______________________________________. a. reducing the effort distance b. increasing the distance through which the force is applied c. reducing the work d. increasing the work

b. increasing the distance through which the force is applied

A force acting on an object does no work if _________________________________________. a. the force is greater than the force of friction b. the force is not in the direction of the object's motion c. a machine is used to move the object d. the object accelerates

b. the force is not in the direction of the object's motion

mechanical energy can be in the form of...

both kinetic and potential energy

which requires more work, lifting a 90 kg sack vertically 6m, or lifting a 45 kg sack vertically 12m?

both require the same about of work

No work is done by gravity on a bowling ball that rolls along a bowling alley because a) no force acts on the ball. b) no distance is covered by the ball. c) the force on the ball is at right angles to the ball's motion. d) no potential energy converts to kinetic energy. e) its kinetic energy may vary.

c) the force on the ball is at right angles to the ball's motion

A 120-m long ski lift carries skiers from a station at the foot of a slope to a second station 40 m above. Whatis the IMA of the lift? a. 40 b. 160 c. 3 d. 0.3

c. 3

Two identical arrows, one with twice the speed of the other are fired into a bale of hay. The faster arrow will penetrate the bale a) the same distance as the slower arrow b) twice as far as the slower arrow c) four times as far as the slower arrow d) more than four times as far as the slower arrow e) none of the above c) four times as far as the slower arrow

c. four times as far

A machine applies a horizontal force to push packed boxes onto a conveyor belt, which carries them across a factory for shipping. Which of the following best describes a direct energy transfer that takes place? a. from machine to conveyor belt b. from conveyor belt to shipping truck c. from machine to box d. from machine to shipping truck

c. from machine to box

The power of a machine measures _____________________________________________. a. the work it does b. the force it produces c.its rate of doing work d. its strength

c. its rate of doing work

The efficiency of a machine is always less than 100 percent because ________________________________. a. the work input is too small b. the work output is too great c. some work input is lost to friction d. a machine cannot have an IMA greater than 1

c. some work input is lost to friction

Work input is greater than output on a shotgun used by a hunter. Which might explain where some of the input went? a. heat b. sound c. friction d. all of the above

d. all of the above

1. The actual mechanical advantage of a machine..... a. cannot be less than 1 b. decreases as the input (effort) distance increases c. increases with greater friction d. is less than the ideal mechanical advantage of the machine

d. is less than the ideal mechanical advantage of the machine

A machine is classified as a compound machine if it ____________________________________________. a. is very efficient b. has an IMA greater than 1 c. has moving parts d. is made up of two or more simple machines that operate together

d. is made up of two or more simple machines that operate together

A wheelbarrow is an example of a(an) _________________________. a. wedge b. inclined plane c. wheel and axle d. lever

d. lever (class 2)

the ratio of useful work output to total work output is called the ______.-lever arm; fulcrum; mechanical advantage; pivot point; efficiency

efficiency

an object at rest may have a. energy b. speed c. velocity d. momentum

energy

an object at rest may have ______-speed; momentum; energy; velocity

energy

A hydraulic press properly arranged, like a simple lever, is capable of multiplying energy input. a) true b) sometimes true c) false

false

T/F: the rate at which work is done is called energy

false

T/F: the ratio of useful work output to total work input is mechanical advantage

false

In physics, work is defined as....?-distance divided by time; force divided by time; force times distance; force times time; force divided by distance

force times distance

how much farther will a car traveling at 100 km/s skid than the car traveling at 50 km/s?-twice as far; half as far; the same distance; four times as far

four times as far

If Nellie Newton pushes an object with twice the force for twice the distance, she does _______. -Twice the work; the same work; four times the work; eight times the work

four times the work

Besides a reduction in friction, the only way to increase the amount of work output of a machine is to_______ the work input.

increase

when a car's speed triples, its kinetic energy...

increases by nine times

The force that is exerted on a machine is called the ______________ force.

input

The SI unit of work is the ____________

joule

potential energy is the energy an object has because of its ______-location; density; temperature; size; speed

location

potential energy is the energy an object has because of its...

location

The __________ of a machine is the number of times that the machine increases the input force.

mechanical advantage

the ratio of output force to input force of a simple machine is called the ________-efficiency; lever arm; fulcrum; mechanical advantage; pivot point

mechanical advantage

an object that has kinetic energy must have...

momentum

an object that has kinetic energy must be...

moving

an object that has linear kinetic energy must be______-at rest; at an elevated position; moving

moving

If you push for an hour against a stationary wall, you do no work a) on the wall. b) at all. c) both d) none of the above a) on the wall.

on the wall

kinetic energy of an object is equal to ______.-its mass multiplied by its acceleration; one half the product of its mass times its speed squared; its mass multiplied by its acceleration squared; its mass multiplied by its speed; one half the product of its mass times its speed

one half the product of its mass times its speed squared

kinetic energy of an object is equal to...

one half the product of its mass times its speed squared

a job is done slowly, and an identical job is done quickly. Both jobs require the same amount of work but different amounts of ______.-energy; power; both power and energy

power

a job is done slowly, and an identical job is done quickly. both jobs require the same amount of work, but different amounts of...

power

Which requires more work: lifting a 50 kg sack vertically 2 m or lifting a 25 kg sack vertically 4 m.

same

which requires more work: lifting a 50 kg sack vertically two meters or lifting a 25-kg sack vertically 4 meters?-lifting the 25-kg sack; lifting the 50 kg sack; same amount of work

same amount of work

A(An) _______________ can be described as an inclined plane wrapped around a cylinder.

screw

which has greater kinetic energy, a car traveling at 80 km/hr or a half-as-massive car traveling at 160 km/hr?

the 160 km/hr car

as a pendulum swings back and forth...

the lowest points have KE, end points is all PE, PE is transformed to KE, KE is transformed to PE all of the above

the amount of potential energy possessed by an elevated object is equal to _______-the work done in lifting it; the force needed to life it; the value of the acceleration due to gravity; the power used to lift it; the distance it is lifted

the work done in lifting it

Energy transforms from one form to another with no net loss or gain.

true

The energy an object has by virtue of it's motion is called it's kinetic energy

true

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

twice as much

if you lift two loads up one story, how much work do you do compared to lifting just one load up one story?-twice as much; one quarter as much; the same amount; four times as much

twice as much

if you lift two loads up one story, how much work do you do compared to lifting just one load up one story?

twice as much work

power is defined as the...

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

all simple machines ideally work on the priciple that _________-work input equals work output; total momentum before a collision equals total momentum after the collision; impulse equals momentum change; kinetic energy transforms into potential energy; force equals mass times acceleration

work input equals work output

In an ideal machine, what does work input equal?

work output

Describe and explain a situation in which work is done, and one in which work is not done

- Work is done when a person kicks a soccer ball (force is applied in the same direction that the ball travels). - Work is not done when a person holds something in his/her hand (force is being applied to hold the object up, but it is not moving).

a girl can easily lift an 80-N rock with the help of a type 1 lever. Whenn she pushes down with 10 M of force, she lifts the rock .1 meters. How far does she move her arms to do this?-10;8; 1; .8; .1

.8

how much work is done on a 50-N rock that you carry horizontally across a 10-m room?-10; 5; 50; 0; 500

0

how much work is done on a 80 N crate that you carry horizontally across a 2m room?

0 J (because of the horizontal direction)