Transcript File
Review Problems: Momentum & Impulse Some Review Which object exerts more force on the other one: A bug hitting a windshield or the windshield hitting the bug? SAME A rocket pushing the fuel out or the fuel pushing the rocket up? SAME Momentum Which object has more momentum: A 65 kg person sitting on the porch or a 0.02 kg bug flying around your head. THE BUG A train with a mass of 350 kg moving at 2 m/s or a car with a mass of 150 kg moving at 25 m/s THE CAR Think back to the web game… What is the difference between an elastic and totally inelastic collision? Elastic they bounce off of each other Inelastic they stick together And our lab… What is the difference between an internal and external force? Give one example of each from the lab with the exploding cars. - Internal are within the system – Cart A pushing on Cart B and Cart B pushing on Cart A - External are from outside factors – Friction acting on the carts Mmm a taste of summer A 2kg watermelon is at rest. Then it explodes because explosions are fun. If the watermelon breaks into two pieces with the same amount of mass what do we know about the velocity of each piece? What about their direction? Velocities are equal but in opposite directions. They originally had a total momentum of zero. That means their total final momentum needs to be zero. If they have the same mass they would have to have the same velocity More Watermelon What would happen to the velocities if one piece had double the mass of the other piece? (in this case one piece has a mass of 2/3 kg and the other one has a mass of 4/3 kg) Then the large piece would to have half of the velocity and the same piece would have to have double the velocity. Baseball (apparently I am in a summer mood) At what speed would a catcher be propelled backwards if he has a mass of 45 kg and catches a 145 g baseball travelling at 40 m/s (90 mph)? = 0.12847 kg m/s Impulse A car is speeding at a rate of 55 m/s when it hits a tree (really guys you need to stop text messaging when you driving). If the car has a mass of 400 kg and it takes .5 seconds to come to a stop, what is the force exerted on the car? =44000 N Now thanks to safety Why is it good for you that the airbag deployed? It increases the amount of time it takes for you to stop. This in turn reduces the amount of force you feel since the change in momentum would be the same. Extra Challenge Two Hockey Pucks are headed towards each other as shown below. If they stick together after the collision what is the speed of two combined. 12.09 kgm/s at 60.3 degrees north of east