Choater 10

Question 1

Energy

Answer 1

Energy is needed to make stationary objects move, to change their
shape, or to warm them up. When you lift an object, you transfer
energy from your muscles to the object.

Question 2

gravitational potential stores

Answer 2

(the position of objects in a gravitational field)

Question 3

kinetic stores

Answer 3

(moving objects)

Question 4

thermal stores

Answer 4

(hot objects)

Question 5

elastic stores

Answer 5

(objects compressed or stretched).

Question 6

Energy pt2

Answer 6

Energy is measured in joules (J). One joule is equal to the energy
needed to raise a 1N weight through a vertical height of 1 m.

Whenever energy is transferred, the total amount of energy atter
the transfer is always equal to the total amount of energy before the
transfer.
The total amount of energy is unchanged.

Energy cannot be created or destroyed.

Question 7

Forces at work

Answer 7

Work is done on an object when a force acting on it makes it move.
As a result, energy is transferred to the object.

The amount of work done depends on the force and the distance the object moved.

The greater the force or the further the distance, the greater the
work done.

Work done = force x distance moved in the direction of the force.

Question 8

Force pt 1

Answer 8

A force of IN is required to raise an object of weight IN steadily.

If it is raised by 1m, the work done by the force is 1J (= IN x 1m).

The gain potential energy of the raised object is 1J.

Question 9

Force pt2

Answer 9

2N object raised to a height of 1 m, the work done, and hence
potential energy of the raised object, is 2J (= 2N x 1 m).

Question 10

To stretch the spring to extension ΔL

Triangle graph

Answer 10

Work done = 1/2 x F x ΔL

Question 11

Kinetic energy

Answer 11

Kinetic energy is the energy of an object due to its motion. The
faster an object moves, the more kinetic energy it has. To see the exact
link between kinetic energy and speed, consider an object of mass m,
initially at rest, acted on by a constant force F for a time t.

Question 12

Kinetic energy equation

Answer 12

Kinetic energy, Ek = 1/2 x m x v²

Question 13

Potential energy

Answer 13

potential energy is the energy of an object due to its position.

If an object of mass m is raised through a vertical height Δh at steady
speed, the force needed to raise it is equal and opposite to its weight mg.

Therefore,

the work done to raise the object = force x distance moved = m x g x Δh

Question 14

The work done on the object increases its gravitational potential energy.

Answer 14

Change of gravitational potential energy = ΔEp= m x g x Δh

Question 15

Involving kinetic and potential

Answer 15

1/2 x m x v² = m x g x Δh

Question 16

Work done =

Answer 16

Force x displacement

Question 17

Work done is

Answer 17

Integral of force with respect of displacement

Question 18

Area of trapezium for graph

Answer 18

A + b / 2 x h

1/2 x h x [ y0 + 2 x (y1 + y2 + y3 … + yn - 1) + yn]

Question 19

Power

Answer 19

Power is the rate of energy transfer

Question 20

Power equation

Answer 20

P = Δe / Δt 
P = power (w) 
E = change in energy (j)
T = change in time (s)

Question 21

Worked example

Answer 21

P = Δe / Δt
= m x g x h / Δt
60 x 9.81 x 4 / 5 = 470w

Question 22

Work done per second =

Answer 22

= force x distance per second

P = f x v

Question 23

Motive power

Answer 23

Energy per second wasted due to the resistive force + the gain of kinetic energy per second

Question 24

Energy and efficiency

Answer 24

When an energy transfer occurs some energy is always wasted

This is usually due to friction which results in heat energy

Efficiency = useful energy transferred / total energy supplied

= work done / total energy supplied

= useful power transferred / total power input