Section 73 Momentum

Momentum = mass x velocity Unit: kg m s-1 or Ns It is a vector quantity. It has magnitude and direction. Jupiter has a mass of 1.8988 x 1027 kg and moves at a speed of 13.7 km/s Momentum = 1.8988 x 1027 x 13700 Momentum = 2.6 x 1031 kg m s-1

Section 74 Investigate and apply the principle of conservation of linear momentum to problems in one dimension http://www.youtube.com/watch?v=yPcaxHkpYQw Introduction to momentum http://www.youtube.com/watch?v=pZqkaJDaz2A&feature=related Pool table http://www.youtube.com/watch?v=2Y57pw_iWlk&feature=related Golf ball http://www.youtube.com/watch?v=9Uc902VRHXI&feature=related Golf ball hitting steel at 150 mph

The principle of the conservation of momentum states: For a system of colliding objects, the total momentum remains constant, provided no external (resultant) forces act on the system. For a linear collision (one dimension) the equation for the principle can be written: http://www.youtube.com/watch?v=YlkTBbFikU8 Examples http://www.youtube.com/watch?v=mFNe_pFZrsA&NR=1 Newton’s cradle http://www.s-cool.co.uk/alevel/physics/momentum-and-impulse/principle-of-the-conservation-of-momentum.html Momentum two cars http://www.youtube.com/watch?v=SBesU12g58I&feature=related The different types of collision

Elastic Collisions M1U1 + M2U2 = MV1 + MV2 In an elastic collision not only is momentum conserved so is the kinetic energy. So: M1U1 + M2U2 = MV1 + MV2 ½ M1U12 + ½ M2U22 = ½ M1V12 + ½ M2V22 are both true The only solution to this is that, both masses are the same (M1 = M2) and one mass is moving, with speed U, before the collision and the other after with speed V, where V=U. An example would be a stationary snooker ball being hit by another snooker ball. In the real world it is very difficult to find elastic collisions.

Inelastic Collisions M1U1 + M2U2 = MV1 + MV2 Most (if not all) collisions are inelastic. In an inelastic collision only the momentum is conserved. Some of the kinetic energy is converted into sound and heat. M1U1 + M2U2 = MV1 + MV2 ½ M1U12 + ½ M2U22 ≠ ½ M1V12 + ½ M2V22 The difference between the total kinetic energy before and the total kinetic energy after is the amount of energy converted into other forms (e.g. Heat and sound). A perfectly inelastic collision occurs when two objects of the same mass and speed collide head on. They will both stop, hence all the kinetic energy is converted into heat and sound.

Section 75 Relate net force to the rate of change of momentum (for situations where mass is constant) Force (net) Applying a force to a mass produces a change in momentum

Questions Q.1 A hockey puck is hit by a hockey player at the goalie. The puck is hit with a 1200 N force. The stick made contact for 0.1 seconds. What impulse was given to the puck? If a goalie stopped it with a force that acts for 0.65 seconds, then what force did he apply? Q.2 A 1000 kg car crashed into a barrier. The car changed speed from 30 m/s to 20 m/s in 2 seconds. What force did the barrier apply to stop the car? Q.3 A 60 kg skateboarder accelerated from 5 m/s to 12 m/s. She applied a force of 4200 N. How quickly did she accelerate? Q.4 A outfielder stops a ball that is originally hit with an impulse of 2000 Ns. The balls mass is 0.25 kg. What was the ball's initial speed ?

Q.5 What impulse is gained by the toy car over the first 5 seconds? 30 N s What is the velocity of the toy car, 0.756 kg, after 5 seconds if it starts from rest? 30.7 m s-1 What is the velocity of the toy car, 0.756 kg, after 20 seconds if it starts from rest? 52.9 m s-1