Energy

Question 1

What is the equation used to work out the distance using acceleration?

Answer 1

(final velocity)2 – (initial velocity)2 = 2 × acceleration × distance

Question 2

What is the thinking distance?

Answer 2

It is the distance travelled during the reaction time

Question 3

What is the stopping distance?

Answer 3

stopping distance = thinking distance + braking distance

Question 4

Why would the stopping distance increase?

Answer 4

as speed has increased

Question 5

What can increase reaction time?

Answer 5

Tiredness
alcohol
drugs
distractions (e.g. mobile phone)

Question 6

What increases braking distance?

Answer 6

wet or icy conditions - reduces the friction between the tyres and the road
worn tyres - reduces the friction between the tyres and the road
worn brakes

Question 7

For the same braking force, explain what happens to the braking distance if the speed doubles.
You should refer to kinetic energy in your answer.

Answer 7

doubling the speed increases the kinetic energy by a factor of 4
the work done by the brakes to stop the car increases by a factor of 4
the braking force is constant, work done is force x distance
so if work done increases by 4 then the braking distance must increase by 4

Question 8

What does work done mean?

Answer 8

work is done when energy is transferred from one store to another

Question 9

What happens during braking?

Answer 9

the force of friction acts between the brake and the wheel
the kinetic energy of the car is converted to thermal energy in the brakes
car slows down as it loses kinetic energy
the greater the speed the greater the braking force
which could cause brakes to overheat

Question 10

What eventually happens to the wasted energy?

Answer 10

It dissipates into the surroundings

Question 11

What is the equation that links energy, power and time?

Answer 11

E = P x t

Question 12

Give one environmental advantage to turning off electrical appliances when they are not being used.

Answer 12

fewer greenhouse gases produced

conservea fossil fuels

Question 13

What is the equation for kinetic energy?

Answer 13

Ek = 1/2 x m x v^2

Question 14

What is the equation for elastic potential energy?

Answer 14

Ep = 1/2 x k x e^2

Question 15

The speed of the miner at the bottom of the slide is much less than the calculated
maximum possible speed.
Explain why.

Answer 15

work is done
against the friction between the miner and the slide
which causes kinetic energy to be transferred as heat
that is lost to the surroundings