Momentum & explosions

1. Rifle

Total momentum of the rifle and the bullet is zero as they are stationary.2.The explosion creates a backward momentum on the rifle. This causes the rifle to recoil backwards.1.When the rifle is fired, the explosion of the gunpowder forces the bullet out of the barrel. A momentum in the forward direction is created.2. Air escapes from a deflating balloon

Total momentum of the balloon is zero as it is stationaryThe balloon shoots upwards, moving with an upward momentumAir has mass and moves with a velocity. This creates a momentum in the downward direction.3. A canon firing a shellIt produces two fragments of masses m (shell) and M (cannon) with velocities u and v respectively.

An explosion is a closed system which does not involve any external force.The total momentum is conserved in an explosion.

Exercise1. The diagram show a boy of 60kg and a girl of 50kg on the roller skates. Initially, they hold each others hand. Then, the boy pushes the girl and both of them release their hands. If the velocity of the girl is 3 ms-1 after being pushed, find the velocity of the boy. (Assume that no frictional force)

2.Jane and John go ice skating. With their skates on, Jane and John push against each other on level ice. Jane, of mass 50kg, moves away at a velocity of 3ms-1 to the right. What is Johns velocity if he is 75kg?

3.Harfeez alight a boat at a velocity of v ms-1 and lands on the dock. The boat bounces backwards with a speed of v. If the masses of Harfeez and the boat are m and 3m respectively, find the speed of the boat (ignoring friction due to water).

Arrangement of apparatus:

Procedure:1.The apparatus is arranged as shown in figure.2.Two trolleys A and B of equal mass are placed in contact with each other on a smooth surface. The spring-loaded piston in trolley B is compressed.3.The release pin on trolley B is given a light tap to release the spring-loaded piston which then pushes the trolleys apart. The trolleys collide with the wooden blocks.4.The experiment is repeated and position of the wooden blocks are adjusted so that both trolleys collide with them at the same time.5.The distance dA and dB are measured and recorded. Note: dA is positive while dB is negative since d, displacement is a vector quantity.6.The experiment is repeated using(a)1 trolley with 2 stacked trolleys(b) 3 stacked trolleys with 1 trolley

Application of the Conservation of Momentum

1. Rocket

A rocket carries liquid hydrogen and liquid oxygen1The mixture of hydrogen fuel and oxygen burns vigorously in the combustion chamber2The gases formed expand rapidly and are forced to discharge through the exhaust nozzle at a high velocity3A backward momentum is created4In accordance with the principle of conservation of momentum, the rocket gains a forward momentum and moves forward at high velocity.52. Jet engine

Air from the atmosphere is drawn into the engine and compressed by a compressor before it is forced into combustion chamber at high pressureIn the combustion chamber, kerosene fuel burns vigorously with the compressed airThe hot gases formed expand rapidly and are forced out of the nozzle at high speed through the turbine which rotates the compressorThe ejected high speed exhaust gases create a backward momentumIn accordance with the principle of the conservation of momentum, a forward momentum for the engine is produced. The plane thus flies forwards.Jet of exhaust gasesMoves forwardsThe principle of the conservation of momentum occurs in nature.Diagram show how does a squid escape.The squid fills its body up with water which it forces through a tube. This makes the squid move on the opposite direction very quickly. This is called jet propulsion.

The shower of burning fragments from an exploding fireworks launched into the sky is governed by the principle of the conservation of momentum. The symmetrical pattern indicates that the total momentum is conserved.

The large volume of water that rushes out from a water hose with a very high speed has a large momentum. In accordance with the principle of conservation of momentum, an equal and opposite momentum is created causing the fireman to fall backwards. Thus, several firemen are needed to hold the water hose.

Exercise1.A pigeon of mass 120 g is flying at a velocity of 2 ms-1. What is its momentum?

2.Calculate the momentum of a car of car of mass 2 000 kg moving with a velocity of 30 ms-1.

3.A bull of mass 250 kg is moving at a momentum of 750 kgms-1. Find its velocity.

4.A bullet with mass of 50 g is fired from a 2 kg pistol with a velocity of 120 ms-1. What is the total momentum of the bullet and the pistol after explosion?

5.During training, Othman fires a pistol of 1.5 kg mass.

A bullet with a mass of 30 g is released at a velocity of 300 ms-1. What is recoil velocity of the pistol?6.A 500 kg car travelling at 30 ms-1 collides with a 3000kg lorry which is at rest. After the collision, both the car and lorry move together. What is the common velocity after the collision?

7.Hizam and his son Jamal are at an ice rink.

Jamal with a mass of 20 kg is moving at a velocity of 2 ms-1 while Hizam with a mass of 60 kg, is directly behind Jamal and moving at 6 ms-1. Hizam decides to pick Jamal up and continues moving without stopping. Determine the final velocity of Hizam and Jamal.8.Trolley A of mass 3 kg moving at 4 ms-1 collides with trolley B of mass 4 kg which is moving in the opposite direction. If both the trolleys move together at 3 ms-1 in the direction of trolley B after the collision, find the initial velocity of trolley B.

9.A butterfly rests on a leaf floating on the surface of a pond.

The butterfly then starts moving to the tip of the leaf at a speed of 5 cms-1 relative to the water. The leaf, in accordance with the principle of the conservation of momentum, moves at 3 cms-1 relative to the water in the opposite direction. If the mass of the leaf is 8g, determine the mass of the butterfly.

10.Boat A and boat B are moving at a speed of 2 ms-1 and 1 ms-1 respectively before the two collide head on. The masses of boat A and B (including the passengers) are 150 kg and 250 kg respectively.

If boat A bounces back with a velocity of 0.5 ms-1, what is the velocity of boat B?11.Sau Fei and Siew Ling, each with a mass of 60 kg and 49.5 kg respectively, are standing at rest on an ice rink. Sau Fei throws a ball of mass 0.5 kg towards Siew Ling.

What is the recoil velocity of Sau Fei if the velocity of the ball is 8 ms-1? What is the velocity of Siew Ling after she receives the ball?