Power, Momentum, Saftey

Question 1

What is power measured in?

Answer 1

Watts

Question 2

One watt = ………….?

Answer 2

One watt= 1 joule of energy

transferred per second

Question 3

A motor transfers 4.8 kj of useful energy in 2 minutes. Find its power output.
P= E/t

Answer 3

P= E/t
4800/120 = 40 W

Question 4

What is the equation of momentum?

Answer 4

Momentum= massXvelocity

kgm/s = Kg X m/s

Question 5

What four car safety measures are used to reduce harm to passengers?

Answer 5

1) crumple zones
2) seatbelt’s
3) Side impact bars
4) airbags

Question 6

What do you crumple zones do and how do they work?

Answer 6

Crumple zones increase the impact time, which decreases the force produced by the change in momentum.
The cars kinetic energy is converted into other forms of energy by the car body as it changes shape

Question 7

How do seatbelt’s reduce the forces acting in the chest?

Answer 7

Seat belts increase the time it takes for the person to stop moving which reduces the forces acting on the chest. They also absorb some of their kinetic energy

Question 8

How do side impact bars work?

Answer 8

They are strong metal tubes fitted into car door panels to direct kinetic energy away from passengers to places such as crumple zones

Question 9

How do brakes reduce the kinetic energy of a car?

Answer 9

By transferring it into heat

Question 10

What do regenerative braking systems do?

Answer 10

Regenerative brakes use the System that drives the vehicle to do the majority of the braking

Question 11

What is an advantage of regenerative brakes?

Answer 11

They store the energy of breaking rather than wasting it

Question 12

Cars are designed to be aerodynamic. What does this mean?

Answer 12

This means that they are shifting in a way that airflows very easily and smoothly pass them to minimise their air resistance

Question 13

What is meant by power in terms of work done?

Answer 13

Power is the rate at which work is done

Question 14

Give the equation for momentum

Answer 14

P= mXv

Question 15

What is meant by the conservation of momentum?

Answer 15

The total momentum before an event is the same as after the event

Question 16

Name to safety features that increase the time taken for the car driver to stop in a collision…

Answer 16

Seatbelt’s airbags crumple zones

Question 17

Give two factors that will affect the top speed of a car…

Answer 17

1) . Power of the engine

2) how aerodynamic the car is

Question 18

What is the equation for power?

Answer 18

Power= work done
__________________

           Time taken

P= E
____

     t

Question 19

Explain why aerodynamic cars tend to have higher top speeds (3)

Answer 19

Air flows easily over aerodynamic cars so there is less air resistance. Cars reach their top speed when the resistive force equals the driving force. With less air resistance to overcome aerodynamic cars can reach a higher speed before this happens

Question 20

Explain how a regenerative braking system works (3)

Answer 20

During breaking the vehicles motor is put into reverse which slows the wheels. This motor acts as an electrical generator and converts kinetic energy into electrical energy, which is stored as chemical energy in the vehicles battery