2a.4 - Power & Car Safety Flashcards
What is power?
Rate of doing work
What is power measured in?
Watts
A motor transfers 4.8kJ of useful energy in 2 minutes. Find its power output
Power = work done% time taken
P= E%t
P = 4800 % 120
= 40 W
What does momentum have?
Size and direction
Momentum before =
= Momentum after
What is a closed system?
Where no external forces act
What causes changes in momentum?
Forces
What are cars designed to do in a crash?
Convert kinetic energy safely
What are examples of how car’s are designed to transfer kinetic energy safely?
- Crumple zones
- Seat belts
- Side impact bars
- Air bags
How do crumple zones improve car safety? (2)
- 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
How do seatbelts improve car safety? (2)
- Stretch slightly to increase the time taken for the wearer to stop
- Some kinetic energy is absorbed by the seat belt
How do side impact bars improve car safety?
They help direct the kinetic energy of the crash away from the passengers
How do air bags improve car safety?
They slow you down more gradually and prevent you from hitting hard surfaces
How do breaks reduce the kinetic energy of the car?
They transfer it to heat and sound energy
What are regenerative breaking systems?
- 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
