Chapter 5 Work, Energy & Power

Question 1

Work Done

Answer 1

is when an object is moved over a distance by an external force applied in the direction of its displacement

Question 2

when work is done

Answer 2

energy is transferred from one object to another -Work done can be thought of as the amount of energy transferred, hence its units are in Joules (J)

Question 3

if a force acts in the direction that an object is moving

Answer 3

then the object will gain energy

Question 4

If the force acts in the opposite direction to the movement

Answer 4

then the object will lose energy

Question 5

The Principle of Conservation of Energy states that

Answer 5

Energy cannot be created or destroyed, it can only change from one form to another -This means the total amount of energy in a closed system remains constant, although how much of each form there is may change

Question 6

Types of energy

Answer 6

-kinetic -gravitational potential -elastic -chemical -nuclear -internal

Question 7

-kinetic energy

Answer 7

energy of a moving object

Question 8

gravitational potential energy

Answer 8

the energy something gains when you lift it up, and which it loses when it falls

Question 9

elastic energy

Answer 9

the energy of a stretched spring or elastic band(sometimes called strain energy)

Question 10

chemical energy

Answer 10

energy contained in a chemical substance

Question 11

nuclear energy

Answer 11

the energy contained within the nucleus of an atom

Question 12

internal energy

Answer 12

the energy something has due to its temperature(or state). (Sometimes referred` to as thermal or heat energy)

Question 13

Energy dissipation

Answer 13

-When energy is transferred from one form to another, not all the energy will end up in the desired form (or place) -Dissipation is used to describe ways in which energy is wasted -Any energy not transferred to useful energy stores is wasted because it is lost to the surroundings -These are commonly in the form of thermal (heat), light or sound energy -What counts as wasted energy depends on the system

Question 14

The efficiency of a system

Answer 14

is the ratio of the useful energy output from the system to the total energy input —-If a system has high efficiency, this means most of the energy transferred is useful —-If a system has low efficiency, this means most of the energy transferred is wasted

Question 15

efficiency = (energy)

Answer 15

useful energy output/ total energy input x100

Question 16

efficiency = (power)

Answer 16

useful power output/ total power input x100

Question 17

Defining Power

Answer 17

• The power of a machine is the rate at which it transfers energy
• Since work done is equal to the energy transferred, power can also be defined as the rate of doing work or the work done per unit time
• The SI unit for power is W-atts (W) where 1 W = 1 J s-1

Question 18

Derivation Moving power

Answer 18

P=F x v

• This equation is only relevant where a constant force moves a body at constant velocity.
• Power is required in order to produce an acceleration
• The force must be applied in the same direction as the velocity

Question 19

work done

Answer 19

W = F x d

Question 20

power (work)

Answer 20

is the change of work power = w/t

Question 21

at constant velocity

Answer 21

d = v x t therefore w = F x v t p= w/t = F x v x t / t

Question 22

GPE = mgh

Answer 22

• Gravitational potential energy is energy stored in a mass due to its position in a gravitational field
• When a heavy object is lifted, work is done since the object is provided with an upward force against the downward force of gravity
• Therefore energy is transferred to the object GPE = M x G x H

Question 23

Kinetic Energy

Answer 23

• Kinetic energy is energy an object has due to its motion (or velocity)
• A force can make an object accelerate; work is done by the force and energy is transferred to the object
• Using this concept of work done and an equation of motion, the extra work done due to an object’s speed can be derived KE = 1/2 x m x v^2

Question 24

GPE v Height graphs

Answer 24