P2.3 Work, Energy And Momentum Flashcards
Name the 9 types of energy
Thermal Light Nuclear Chemical Elastic potential Gravitational potential Kinetic Electricity Sound
What does it mean if an object has done work?
It has transferred energy
What’s work done measured in?
Joules (J)
How do you work out work done?
Force X distance
How do you work out power?
Work done/time
What’s power measured in?
Watts (W)
What objects have gravitational potential energy
Any object that’s raised above the ground
How’d you work out GPE?
Mass X gravitational field strength X height
What’s gravitational potential energy measured in?
Joules (J)
What’s gravitational field strength measured in?
N/kg
What objects have kinetic energy?
Any object that moves
How do you work out kinetic energy?
1/2 X mass X velocity squared
What’s kinetic energy measured in?
Joules (J)
What objects have momentum?
Any object that moves
How do you work out momentum?
Mass X velocity
What’s momentum measured in?
kgm/s
What’s the conservation of momentum?
The total momentum before an event = the total momentum after an event
A railway engine of mass 800kg travelling at 5m/s collides with and becomes attached to a truck of 200kg travelling at 2m/s. Calculate the speed of the truck and engine after the collision.
Before: (800x5)+(200x2) = 4400 kgm/s
After: 4400kgm/s
800+200 = 1000kg
V=P/m 4400/1000 = 4.4 m/s
--------A 0.5 kg trolley is pushed at a velocity of 1.2 m/s into a stationary trolley of mass 1.5 kg. The two trolleys stick to each other after the impact. Calculate the momentum before the collision and the velocity of the two trolleys.
P=VxM
=1.2 X 0.5 = 0.6 kgm/s
V= p/m
= 0.6/ (0.5+1.5)
=0.6/2
=0.3 m/s
How do you calculate force?
Change in momentum/time
When a force is applied to an object, the objects _________ changes. This means _________ also changes.
Velocity
Momentum
How do seat belts provide car safety?
Seat belts work by stopping you from flying forward and hitting the windscreen or seat in front. In a collision they stretch slightly, which prolongs the time it takes for you to stop. This therefore reduces the size of the force on the body.
How do airbags create car safety?
Airbags inflate almost instantly in a collision. They provide a soft cushion for your face and chest, and spread the force of impact over a larger area. Some cars also have airbags in the side to protect against side-impact collisions.
How do crumple zones make car safety?
They’re in the front rear of the car and are designed to crumple gradually during a collision. This increases the duration of the collision, which reduces the size of the force and also absorbs some of the energy of the impact.
What do side/impact bars do to make a car safer?
The bars absorb some energy of the collision so the car doesn’t crush into you sideways and stops the energy being passed onto you.
What do normal brakes do?
When the brakes are applied work is done to slow the car down
The brakes reduce the kinetic energy by transferring it to heat energy (it’s wasted)
What do regenerative brakes do?
Uses the drive system to brake
The brakes put the motor into reverse (when the motor runs backwards the wheels are slowed)
The motor acts as an electric generator - converting kinetic energy into electrical energy
This is stored as chemical energy in the battery
What’s better about regenerative braking compared to normal braking?
Regenerative braking transfer energy whereas normal breaking wastes it
Why is an aerodynamic vehicle good?
Means less air resistance so higher speed before the forces balance
Quicker
