Momentum

momentum is always conserved (saved)

Momentum depends upon the mass and velocity of an object

p = M x V

Kg m/s

.A car of mass 1000kg travelling at a velocity of 15 m/s?

A horse of mass 500kg running at a velocity of 20 m/s?

.A car of mass 1000kg with a momentum of 15,000 kg m/s?

.A person of mass 75kg with a momentum of 112.5 kg m/s?

As long as there are no external forces acting on the objects then momentum will always be conserved in a collision. 

Total momentum before a collision = 0

Total momentum after a collision = 0

Firstly: work out the total momentum before the crash.

= (m1 x v1 ) + (m2 x v2 )

= (12,000 x 5) + (12,000 x 0)

= 60,000 + 0

= 60,000 kg m/s

Secondly: work out the total momentum after the crash.

= (m1 x v1 )  + (m2 x v2 )

= (12,000 x 0) + (12,000 x v2 )

= 0 + (12,000 x v2 )

= 12,000 x v2

S0................

Rearrange to find Velocity - V = p / M

V2  = 60,000 / 12,000 

V2  = 5 m/s

A bullet of mass 10g is fired from a 6kg rifle at a speed of 300m/s. What is the recoil velocity of the rifle?

Momentum before = 0

Momentum after firing = momentum bullet + momentum rifle = 0

p= M x V + M x V

p = M xV + M x V

p = 0.01 x 300 + 6 + 0

p = 3 Kg m/s

Now find the Velocity of the rifles recoil - the rifle and the bullet now have a combined mass!!

Momentum before a collision must be the same as momentum after a collision

This only applies to closed systems (no external force is acting on the objects)

Momentum has a + or - direction

A trolley of mass 4kg moving at 10 m/s collides with a 2 kg trolley moving in the same direction at a velocity of 4m/s. they separate after the collision and the 4 kg trolley slows to 7m/s. What is the final speed of the other trolley?

DRAW THIS OUT AS WE GO THROUGH IT

Work out the momentum of each trolley

p= M1 x V1

p = M2 x V2

What is the combined momentum of the trolleys?

p = M x V

Remember that total momentum MUST BE CONSERVED

The new Momentum of trolley 1 is 28 Kg m/s

What must the new momentum of trolley 2 be?

V = p/M

When a force is applied to an object, the velocity of that object will change.

This means that the momentum will also change

The change of momentum depends upon the size of the force and the length of time that force was applied for.

Change in momentum = Force x time

Δp = F x t

REMEMBER

p = M x V

Change in momentum = p2 - p1

A rugby ball of mass of 0.5 Kg is kicked from stationary to a velocity of 8 m/s. The kickers foot is in contact with the ball for 0.1 seconds.

What force does the kicker use?

F = Δp / t

F = (0.5 x 8) - (0.5 x 0) = 4

4/0.1

Force = 40 N

A tennis ball is rolled at a toy car of a mass 0.1 Kg. The car is moved with a velocity of 0.5 m/s

If the car and the ball are in contact for 0.01 seconds, what Force was the balled rolled with?

F = Δp / t

F = (0.1 x 0.5) - (0.1 x 0) = 0.05

0.05 / 0.01

Force = 5 Newton