Work, Energy And Power

Question 1

Define work done

Answer 1

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

Question 2

Define the joule

Answer 2

1 joule is the amount of work done when 1 newton moves through 1 metre

Question 3

Define the watt

Answer 3

1 watt is the power when 1 joule is transferred in 1 second

Question 4

Define power

Answer 4

Power = work done / time

Question 5

Derive P = Fv

Answer 5

P = W/t
P = Fx/t
P = F(x/t)
P = Fv

Question 6

What types does energy come in?

Answer 6

Kinetic energy
Gravitational potential energy
Elastic potential energy

Question 7

State the properties of energy

Answer 7

• energy is conserved: in a closed system, the total energy is constant
• energy is transformed from one type to another
• the amount of energy transferred = work done

Question 8

What are the two main equations for work done?

Answer 8

W = Fx

and W = Fxcos θ

Question 9

What is the equation for work done when accelerating an object with a force?

Answer 9

W = 1/2mv^2

Question 10

What is the equation for work done when lifting an object?

Answer 10

W = mgh

Question 11

What equation can you use to work out the final velocity of a falling object?

Answer 11

√2gh —> v

Question 12

What equation can you use to work out the height that a launched object will reach?

Answer 12

v^2/2g —> h

Question 13

What are all the different ways you can find work done?

Answer 13

• Fxcos θ
• Pt
• Fvt
• IVt
• change in Ep
• change in Ek
• Fd
• energy transferred

Question 14

How do you calculate the efficiency of a mechanical system?

Answer 14

efficiency = (useful output energy/total input energy) x 100