Science Chapter 3

Question 1

Define work

Answer 1

Work is the transfer of energy that occurs when a force is applied over a distance.

Question 2

Give the work equation

Answer 2

Work (in joules) = force (in newtons) x distance (in meters)

W=Fd

Question 3

Define power

Answer 3

Power-the rate at which work is done.

Question 4

Give the power equation

Answer 4

power (in watts) = work (in joules)/time (in seconds)

P=W/t

Question 5

Lifting a stone block 146m to the top of the Great Pyramid required 146,000 J of work. How much work was done to lift the block halfway to the top?

Answer 5

73,000 J

Question 6

Explain horsepower

Answer 6

Watt needed a way to measure the power in his new steam engine. He calculated a horse walking around a circle at a fabric mill, and found that it takes the horse 33,000 foot-pounds per minute. This became 1hp.

Question 7

Define mechanical advantage

Answer 7

A machine’s mechanical advantage is the ratio of a machine’s output force to the input force applied.

Question 8

Give the mechanical advantage equation

Answer 8

mechanical advantage (no units) = output force (in newtons)/input force (in newtons)

MA=F(out)/F(in)

Question 9

Define efficiency

Answer 9

The efficiency of a machine is the ratio of the output work to the input work.

Question 10

Give the efficiency equation

Answer 10

efficiency (in %) = output work (in joules)/input work (in joules) x 100%

efficiency=W(out)/W(in) x 100%

Question 11

Which machine efficiency is impossible?

Answer 11

100%

Question 12

Define simple machines

Answer 12

Simple machines do work using only one movement.

Lever, wheel and axle, inclined plane, wedge, screw, and pulley.

Question 13

Define a lever

Answer 13

Lever-a simple machine made up of a bar that pivots, or rotates, about a fixed point.

Question 14

Define fulcrum

Answer 14

The point about which a lever pivots is called a fulcrum.

Question 15

Give the equation for the ideal mechanical advantage of levers

Answer 15

ideal mechanical advantage = length of input arm (in meters)/length of output arm (in meters)

IMA=L(in)/L(out)

Question 16

Define a wheel and axle

Answer 16

A wheel and axle is an axle attached to the center of a wheel and both rotate together.

Question 17

give the equation for the ideal mechanical advantage of wheel and axle

Answer 17

ideal mechanical advantage = radius of wheel (in meters)/radius of axle (in meters)

IMA=r(wheel)/r(axle)

Question 18

Define an inclined plane

Answer 18

A ramp, or inclined plane, is a flat, sloped surface.

Question 19

Give the equation for the ideal mechanical advantage of an inclined plane

Answer 19

ideal mechanical advantage = length of inclined plane (in meters)/height of inclined plane (in meters)

IMA=l/h

Question 20

Define a wedge

Answer 20

A sloped surface that moves is called a wedge.

Question 21

Define a screw

Answer 21

A screw is an inclined plane wrapped around a cylinder.

Question 22

Define a pulley

Answer 22

A pulley-a simple machine that is a grooved wheel with a rope or a cable wrapped around it.

Question 23

Identify the simple machine in which the fulcrum is between the input force and the output force.

Answer 23

Lever

Question 24

Calculate the ideal mechanical advantage of a ramp with a 24-mm radius handle and an 8-mm radius shaft.

Answer 24

3

Question 25

Which must be true when work is done?

Answer 25

An object moves in the same direction as a force exerted on it.

Question 26

What compound machine uses a lever, wheel and axle, and an inclined plane?

Answer 26

Can opener

Question 27

Give an example of a 1st class lever

Answer 27

Crow bar

Question 28

Give an example of a 2nd class lever

Answer 28

Wheel barrow

Question 29

Give an example of a 3rd class lever

Answer 29

Rake

Question 30

Give an example of a wheel and axle

Answer 30

Screw driver

Question 31

Give an example of an inclined plane

Answer 31

ramp

Question 32

Know the three changes a simple machine offers

Answer 32

Change in force
Change in direction
Change in distance

Question 33

A pulley is often referred to as a

Answer 33

Block and tackle

Question 34

How do you find the mechanical advantage of a pulley?

Answer 34

Count the number of ropes moving upwards, disregard the rope you are pulling down. If you are pulling a rope up, still count it.