a2 unit4 02 momentum

8/13/2019 A2 Unit4 02 Momentum

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Which is more effective at demolishing a wall?

A 1kg metal ball moving at 50ms-1

Or a 1000kg ball moving at 1ms-1

Newton realised that what happens to a movingobjects involved in a collision depends upon two

things :

Mass of the object

Velocity of the object


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Newton used the concept of momentum to

explain the results of collisions

Momentum = mass x velocity

p = m v

Units :

p (kg ms-1) = m (kg) x (ms-1)

Note since velocity is a vector quantity, (both

magnitude and direction) then momentum is also

a vector quantity


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When objects collide, assuming that there are no

external forces, then momentum is alwaysconserved.... Definition :

When two or more objects interact, the total

momentum remains constant provided thatthere is no external resultant force

Mass 75 kg

Velocity 4 ms-1Mass 50 kg

Velocity 0 ms-1

Mass 125 kg

Velocity ??? ms-1


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When objects hit each other the resulting

collision can be considered to be either elastic orinelastic. Momentum and totalenergy are always

conserved in both cases.

Elast ic : momentum conserved, k ineticenergy conserved, total energyconserved

Inelastic : momentum conserved, k ineticenergy NOTconserved, total energy

conserved

In an Inelast ic col l is ion some of the kinetic energy is

converted to o ther forms of energy (of ten heat & Sound)


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Is the following collision elastic or inelastic?

A toy lorry of mass 2kg is travelling at 3ms-1and crashes into a smaller a toy car with a

mass of 800g which is travelling at 2 ms-1in the

same direction as the lorry. The velocity of thelorry after the collision is 2.6 ms-1. What is the

velocity of the car after the collision and is the

crash elastic or inelastic?


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Mass 2 kg

Velocity 3 ms-1

Mass 800 g

Velocity 2 ms-1

Mass 800g

Velocity 3 ms-1

Mass 2 kg

Velocity 2.6 ms-1

Lorry Ek = x 2 x (3)2

Lorry Ek= 9J

Car Ek = x 0.8 x (2)2

Car Ek= 1.6J

Total Ek before = 10.6J

Lorry Ek = x 2 x (2.6)2

Lorry Ek= 6.76J

Car Ek = x 0.8 x (3)2

Car Ek= 3.6J

Total Ek after= 10.36J

Total Ek before Total Ek after

Inelastic Collision

Where is the energy likely to have

gone?


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Two trolleys on an air track are fitted with

repelling magnets. The masses are 0.1kg and0.15kg respectively. When they are released the

lighter trolley moves to the left at 0.24ms-1. What

is the velocity of the heavier trolley

A ball of 0.6kg moving at 5ms-1collides with a

larger stationary ball of mass 2kg. The smaller ball

rebounds in the opposite direction at 2.4ms-1

Calculate the velocity of the larger ball

Is the Collision elastic or inelastic. Explain your

answer

a2 unit4 02 momentum

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