Section 1: Momentum Flashcards
What determines how large a force you need to apply to alter a motion of an object?
- How quickly you want to stop it
- Its velocity
- Its mass
Equation for Momentum
momentum = mass x velocity
kgm/s kg m/s
Factors affecting the thinking distance
- tiredness
- intoxication
- influence of drugs
Factors affecting the braking distance
- wet/icy road surface
- condition of brakes + tyres
Newton’s 1st law
An object stays stationary unless acted on by an external force
Newton’s 2nd law
F = ma (acceleration = rate of change of velocity)
Newton’s 3rd law
For every action there is an equal and opposite reaction
What equation links force, momentum and time?
F = △P/△t
F = ma a = (v - u)/ t
therefore: F = m (v - u)/t
F = (mv - mu)/ t
How to calculate the change in momentum?
△P = mv-mu
final mom - initial mom
For a given momentum change, how can the force be reduced?
Increase the time it takes for the momentum of an object to change to reduce the force it experience.
F =△P
time take
Why does the surface of a playground have a rubbery surface?
Rubbery surfaces can compress, thus increasing the time taken to change momentum of a child if they fall
Why do cars have:
a) an airbag?
b) a seatbelt
c) crumple zone?
- airbags inflate to increase the impact time, reducing the rate of change of momentum of the head as well as spreading the force over a large area
- seat belts are designed to stretch, lowering the rate of change of momentum
- crumple zones increase the impact time
Elastic collision
Momentum is conserved and no kinetic energy is lost
particles collisions
Conservation of momentum
The total momentum before a collision is the same as after
Inelastic collision
Momentum is conserved but some kinetic energy is transferred
(usually everyday collisions)
Work out the velocity of the recoil of the gun if:
- the gun has mass of 2 kg
- it fires a bullet of 10 g that travels 260 m/s
*explosion type question
momentum before = momentum after
momentum of gun = 0
- 01 x 260 = 2.6
- 6 / 1.99 = 1.3 m/s
What’s the equation linking kinetic energy, mass and speed?
KE = 1/2 x mv2
How do jets and rockets fly?
Jet + rocket engines burn fuel which produces high pressure exhaust gases which escape through the back, exerting a force.
The reaction force of the exhaust gas on the vehicle pushes it forward
If 2 forces are a Newton’s 3rd law pair of forces they must
- equal in size
- oposite in direction
- same type of force
- acting on 2 objects
action/ reaction force when Eskimo pushes box on ice
Eskimo pushes box forward, the box pushes back in equal force and opposite direction
Why do weapons have a recoil?
Due to Newton’s 3rd law, when a bullet is fired from the gun the bullet also exerts an equal and opposite force on the gun, causing it to move back. This shows momentum is a vector quantity
What is momentum
Momentum is a quantity possessed by masses in motions
It’s a measure of how difficult it is to stop something from moving
