P5 Momentum (page 216) Flashcards
What is Momentum?
Momentum is mainly about how much ‘oomph’ an object has. It’s a properly that all moving objects have.
Momentum = Mass x Velocity
The greater the mass of an object, or the greater its velocity the more what? the object has?
the more momentum has.
Momentum is a vector quantity, what do this mean?
it has size and direction.
How do you work out the momentum of an object?
P=mv
momentum (kg m/s) = mass (kg) x velocity (m/s)
A 50 kg cheetah is running at 60 m/s. Calculate its momentum?
p= mv = 50 x 60
= 3000 kg m/s
A boy has a mass of 30 kg and a momentum of 75 kg m/s. Calculate his velocity?
v = p ÷ m = 75 ÷ 30 = 2.5 m/s
Momentum BEFORE =?
Momentum AFTER
What is a conservation of momentum mean?
it means in a closed system, the total momentum before an event (e.g. a collision) is the same as after the event.
(a closed system is just a fancy way of saying that no external forces act).
What is meant by momentum is conserved?
e.g. in snooker, balls of the same size and mass collide with each other. Each collision is an event where the mementum of each ball changes, but the overall momentum stays the same (momentum is conserved)
Look at the BEFORE diagram and explain its momentum (on page 216)
The red ball is stationary, so it has zero momentum. The white wall is moving with a velocity v, so has a momentum of p = mv
Look at the AFTER diagram and explain its momentum o(n page 216).
the white ball hits the red ball, causing it to move. The red ball now has momentum. The white ball continues moving, but at a much smaller velocity (and so a much smaller momentum). The combined momentum of the red and white ball is equal to the original momentum of the white ball, mv.
A moving car hits into the back of a parked car. The crash causes the two cars to lock together, and they continue moving in the direction that the original moving car was travelling, but at a lower velocity.
Explain the BEFORE momentem?
Explain the AFTER momentem?
BEFORE: the momentum was equal to mass of moving car x its velocity.
AFTER: the mass of the moving object has increased, but its omentum is equal to the momentum before the collision. So an increase in mass causes a decrease in velocity.
If the momentum BEFORE an event is ZERO, then what will the momentum AFTER be?
it will also be zero.
e.g. in an explosion, the momentum before is zero, after the explosion, the pieces fly off in different directions, so that the total momentum cancels out to zero.
Calculate the momentum of a 60 kg woman running at 3 m/s (2 marks)
p = mv = 60 x 3 (1 mark). = 180 kg m/s (1 mark)
Describe how momentum in conserved by a gun recoiling (moving backwards) as it shoots a bullet (4 marks)
Before the gun fires the bullet, the total momentum is zero (neither the gun nor the bullet are moving) (1 mark). When the bullet leaves the gun, it has momentum in one direction (1 mark). The gun moves backwards so it has momentum in the opposite direction (1 mark). This means that the total momentum after the bullet has been fired is zero. Momentum has been conserved (1 mark).
