2a.4 - Power & Car Safety

Question 1

What is power?

Answer 1

Rate of doing work

Question 2

What is power measured in?

Answer 2

Watts

Question 3

A motor transfers 4.8kJ of useful energy in 2 minutes. Find its power output
Power = work done% time taken

Answer 3

P= E%t
P = 4800 % 120
= 40 W

Question 4

What does momentum have?

Answer 4

Size and direction

Question 5

Momentum before =

Answer 5

= Momentum after

Question 6

What is a closed system?

Answer 6

Where no external forces act

Question 7

What causes changes in momentum?

Answer 7

Forces

Question 8

What are cars designed to do in a crash?

Answer 8

Convert kinetic energy safely

Question 9

What are examples of how car’s are designed to transfer kinetic energy safely?

Answer 9

• Crumple zones
• Seat belts
• Side impact bars
• Air bags

Question 10

How do crumple zones improve car safety? (2)

Answer 10

• The car’s kinetic energy is converted into other forms of energy as the car changes shape
• Crumple zones increase the impact time, decreasing the force produced by the change in momentum

Question 11

How do seatbelts improve car safety? (2)

Answer 11

• Stretch slightly to increase the time taken for the wearer to stop
• Some kinetic energy is absorbed by the seat belt

Question 12

How do side impact bars improve car safety?

Answer 12

They help direct the kinetic energy of the crash away from the passengers

Question 13

How do air bags improve car safety?

Answer 13

They slow you down more gradually and prevent you from hitting hard surfaces

Question 14

How do breaks reduce the kinetic energy of the car?

Answer 14

They transfer it to heat and sound energy

Question 15

What are regenerative breaking systems?

Answer 15

• They put the motor into reverse which slows the wheels.
• The motor acts as an electrical generator converting kinetic energy into electrical energy which can power the battery when stored as chemical energy

Question 16

What is an aerodynamic car?

Answer 16

A car that minimises air resistance