Power, Momentum, Saftey Flashcards
What is power measured in?
Watts
One watt = ………….?
One watt= 1 joule of energy
transferred per second
A motor transfers 4.8 kj of useful energy in 2 minutes. Find its power output.
P= E/t
P= E/t 4800/120 = 40 W
What is the equation of momentum?
Momentum= massXvelocity
kgm/s = Kg X m/s
What four car safety measures are used to reduce harm to passengers?
1) crumple zones
2) seatbelt’s
3) Side impact bars
4) airbags
What do you crumple zones do and how do they work?
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
How do seatbelt’s reduce the forces acting in the chest?
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
How do side impact bars work?
They are strong metal tubes fitted into car door panels to direct kinetic energy away from passengers to places such as crumple zones
How do brakes reduce the kinetic energy of a car?
By transferring it into heat
What do regenerative braking systems do?
Regenerative brakes use the System that drives the vehicle to do the majority of the braking
What is an advantage of regenerative brakes?
They store the energy of breaking rather than wasting it
Cars are designed to be aerodynamic. What does this mean?
This means that they are shifting in a way that airflows very easily and smoothly pass them to minimise their air resistance
What is meant by power in terms of work done?
Power is the rate at which work is done
Give the equation for momentum
P= mXv
What is meant by the conservation of momentum?
The total momentum before an event is the same as after the event
Name to safety features that increase the time taken for the car driver to stop in a collision…
Seatbelt’s airbags crumple zones
Give two factors that will affect the top speed of a car…
1) . Power of the engine
2) how aerodynamic the car is
What is the equation for power?
Power= work done
__________________
Time taken
P= E
____
t
Explain why aerodynamic cars tend to have higher top speeds (3)
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
Explain how a regenerative braking system works (3)
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
