Topic 4 - Momentum, Energy, Work and Power Flashcards
What is stopping distance made up of?
The sum of thinking distance and breaking distance
What factors affect thinking distance?
Reaction time (affected by tiredness, drugs, alcohol, old age, careless attitude) How fast you are going
What factors affect breaking distance?
How fast you are going.
The mass of your vehicle (heavier vehicle takes longer to stop)
How good your breaks are.
How good the grip is (this depends on road surface, weather conditions, and tyres)
What is conservation of momentum?
Total momentum after is the same as before.
How do you work out the total momentum of two ice skaters?
add together their individual momentums.
How do you calculate force?
Change in momentum/time
What is momentum measured in?
Kg m/s
what will the force be like if a change in momentum happens in a short time?
large force
What will the force be like if it happens in a longer time?
Smaller force
How does a crumple zone protect passengers in a car?
it increases the amount of time it takes for the car to stop so therefore decreasing the force that acts upon the passengers
How do seat belts protect people?
they slightly stretch increasing the time taken of the wearer to stop, this reduces the force acting on the chest.
How does bubble wrap work?
it increases the time over which any forces acting on the things inside occur so therefore decreases the force.
Explain what happens when a force moves an object
Energy is transferred and work is done.
Explain what work done means in terms of energy
Energy is transferred.
What is the unit of work?
Joules (J)
What is power?
rate of doing work
What is the formula for power?
Power = work done/time taken
What is power measured in?
Watts (W) or J/s
Define kinetic energy
energy of movement
explain why the kinetic energy of a car is related to the work done by the brakes to stop the car
Initial kinetic energy = work done by brakes to stop vehicle
State the formula relating braking force and breaking distance to mass and velocity
f x d = 1/2 x mass x velocity^2
What is gravitational potential energy?
Energy due to height
what is the approximate gravitational field strength on earth?
10N
State the principal of conservation of energy
energy can never be created nor destroyed - only transferred from one form to another.
Describe the most important energy transfer when a book falls off a shelf
GPE gets transferred to KE
What type of energy is always produced in an energy transfer?
thermal
explain how to relate the gain in KE to the loss in GPE
KE gained = GPE lost
