1. Exam Review Exam 4 Momentum Second 6-weeks, Test 1

2. Question #1 Why can rocket can fly into space, when there is no air to push against? A propeller airplane pushes against the air to make it go. In the 1940’s, a major newspaper published an article, saying space flight couldn’t work without air to push against, but even Newton would have known better. Why? The rocket pushes the exhaust backward, and the equal and opposite reaction pushes the rocket forward. Newton’s Third Law

3. Questions #2 & 3 Define Newton’s Third law of motion: Think!! For every action force there is an equal reaction force in the opposite direction These are “Force Pairs” – Action and Reaction (#3) They are operating in two opposite directions and are operating on two different objects (Newton’s 3 rd Law)

4. Question #4 If every action force has an equal but opposite reaction force, how can two interacting objects be affected differently? The action and reaction forces are operating on different objects. That means they can have different effects, because the masses of the two objects don’t have to be the same. These forces are always equal in magnitude, but operating in the opposite direction from each other

5. Question #5 The momentum of an object depends on what two factors? Let’s look at the equation P = m  v “m” is mass “v” is velocity (speed) that’s it

6. Question #6 What is the momentum of a 0.8-kilogram dodge-ball moving at 10 m/s? P=M=V=P=M=V= ? 0.8 kg 10 m/s

7. Question #7 A rock falls from a cliff, and reaches a velocity of 1.5 m/s when it strikes the hood of a car parked below. The mass of the rock is 1.2 kg. What was the momentum of the rock when it hit the car? P=M=V=P=M=V= ? 1.2 kg 1.5 m/s

8. Question #8 A boy and the skateboard on which he is standing have a combined mass of 75 kilograms. He throws a 2-kg ball forward at 15 m/s. At what speed will the boy roll backward? (75 kg)*v 1 = - (2 kg) * (15 m/2) v 1 = - (2 kg) * (15 m/2) / 75 kg v 1 = -4.4 m/s Momentum 1 = Momentum 2 (in the other direction)

9. Questions #9 & #10 If two kids shove each other and one is more massive than the other, describe how their accelerations compare? Describe those same kids’ momentum: Force = m X a If the force must be the same, then the acceleration must be different If mass goes up, acceleration goes down, so the acceleration of the more massive kid is less P 1 = -P 2 They have the same momentum, but in opposite directions

10. Question #11 What is the momentum of a 5000-kg truck traveling at 30 m/s? P=M=V=P=M=V= ? 5000 kg 30 m/s

11. Question #12 The momentum of a baseball thrown by the pitcher is 6 kg·m/sec. It is stopped by the catcher in 0.01 seconds. a) What equation should be used to solve this equation? b) How much force did the catcher exert to catch the ball? Equation #4,Force = momentum / time

12. Question #13 A ball of mud is thrown with a momentum of 0.6 kg·m/sec and is stopped when it hits a wall in 0.01 seconds. What is the force exerted by the wall when it strikes? Equation #4,Force = momentum / time

13. Question #14 A boy on a bicycle has a velocity of 3 m/s and a combined mass of 65-kg. When he puts on the brakes, friction exerts a force that stops him is 5 seconds. How much is the average force produced by the brakes? Part 1: Find Momentum Part 2: Find Force

14. Question #14 If a 4-kg cannonball was fired at 40 m/s from a 400-kg cannon, the correct equation to determine the velocity of the cannon would be: Equation # 5 See if you can solve for the velocity of the cannon on your own

15. Question #16 A 2-kg model rocket is traveling from its launch pad at a speed of 50 m/s. At what speed would 0.2 kg of gases be expelled from the rocket?

16. Question #17 A 5-kg fire extinguisher is goes off by itself. If it shoots 2-kg of gas at a speed of 30 meters per second, determine the extinguisher’s velocity?: