Which graph represents the motion of a ball rolling on a level friction free track? Which graph represents the motion of a ball rolling down a ramp?

1. Answers 3 & 4 2. Answers 1

Differentiate the motion shown in graphs 1 & 2.

3. Graph #1, the object begins at rest and moves in the positvie direction with increasing velocity. Its speed is increasing. Graph #2, the object begins with a positive velocity, moves in the positive direction and its velocity is decreasing. Its speed is decreasing. Graph #3, the object is moving in the positive direction with constant velocity. Graph #4, the object is moving in the negative direction with constant velocity.

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It slows down the bottom block and speeds up the top block 10. It slows down the bottom block and speeds up the top block

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13. A super-ball will bounce back. It will have a larger change in velocity and as a result a larger impulse.

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14. It will have a larger change in velocity and as a result a larger impulse. This impulse will happen over a smaller time creating a larger force.

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15. The one on the dipped track will speed up as it descends and then have a higher average speed over the next horizontal section. As a result it will have a higher average speed over the length of the track.

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16. Elastic energy converts into gravitational energy. If the spring is compressed ½ as much it will store ¼ the energy. This energy converts into gravitational energy which is directly proportional to height.

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17. Momentum is conserved. (1 kg)(10 cm/s) = (3 kg)(v)

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18 The momentum is case i) is equal to m√2gh and in case ii) is equal to zero.

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19 It will follow path 4 The object must have a force pushing toward the center to go in a circle. If the center pushing force is removed the object will have the velocity at that instant in time which is tangent to the path.

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20 5 The force of gravity provides the unbalanced force toward the center necessary to cause circular motion. This causes the moon to travel in a circle instead of a straight line. It has an appropriate tangential velocity.

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21 The astronaut appears to be floating because he is continuously falling around the earth. The force of gravity is a centripetal force and there is no normal force. All objects are falling at the same rate.

What is the acceleration due to gravity on Planet X? 22 On planet X, a cannon ball is fired straight upward. The position and velocity of the ball at many times are listed below. Note that we have chosen up as the positive direction. Time(s) Height(m) Velocity(m/s) 20 1 17.5 15 2 30 10 3 37.5 5 4 40 -5 6 -10 7 -15 8 -20 What is the acceleration due to gravity on Planet X? A) -5m/s2 B) -10m/s2 C) -15m/s2 D) -20m/s2 E) None of these.

22 5 m/s2

Which statement is true: 23 The graph show positions as a function of time for two trains running on parallel tracks. Which statement is true: At time tC, both trains have the same velocity. Both trains speed up all the time. Both trains have the same velocity at some time before tC. At some time, both trains have the same acceleration. None of the above statements is true. © Eric Mazur, "Peer Instruction" 1997

Both trains have the same velocity at some time before tC. 23 Both trains have the same velocity at some time before tC.

A ball is thrown straight up. At the top of its trajectory, its 24 A ball is thrown straight up. At the top of its trajectory, its velocity is zero, acceleration is zero. velocity is non-zero, acceleration is non-zero. velocity is zero, acceleration is non-zero. velocity is non-zero, acceleration is zero. © Eric Mazur, "Peer Instruction" 1997

velocity is zero, acceleration is non-zero. 24 velocity is zero, acceleration is non-zero.

25 A truck traveling at 50 km/hr approaches a car stopped at a red light. When the truck is 100m from the car, the light turns green and the car immediately begins to accelerate at 2.00m/s2 to a final speed of 100 km/hr. Which graph belows represents this situation? A) B) C) D)

25 B

A): doubles. B): increases by a factor of 4. C): Neither of these. 26 A ball is fired from a canon straight upward with an intial velocity vo. Assume no air resistance. If the intial velocity vo is doubled, the time to reach the apex of the trajectory.. A): doubles. B): increases by a factor of 4. C): Neither of these. D): Impossible to tell from the information given. If the intial velocity vo is doubled, the maximum height of the ball..

B): increases by a factor of 4. 26 A): doubles. B): increases by a factor of 4.

27 A projectile is fired up at |V0 |=10 m/s. Choose up as (+) direction; ground as y=0. What time does it take to reach ymax, the maximum height? 0 s 1 s 2 s 5 s None of these

27 1 second

28 A car of mass m, traveling at constant speed, rides over the top of a hill. The magnitude of the normal force N of the road on the car is.. greater than the weight of the car, N > mg. equal to the weight, N = mg. less than the weight, N < mg.

C: less than the weight, N < mg. 28 C: less than the weight, N < mg.

29 An object is being lowered on a cord at a constant speed. How does the tension T in the cord compare to the weight mg of the object? T = mg T > mg T < mg

29 T = mg

30 An object is being lowered on a cord at a speed which is decreasing. There are two forces on the object, the weight, magnitude mg, and the tension, magnitude T, in the cord. Which equation is true: T = mg T > mg T < mg

30 B: T > mg

31 An elevator is going up at a constant speed. Near the top floor, it starts to slow to a stop. During the period that it is slowing down, its acceleration is A) downward B)  upward. C)  in some other direction.

31 downward

A) 32 RI-4. An object's acceleration vs. time is:                                                                           Which graph best represents the object's velocity vs. time? B) A) A)  D) C) E)

32 B

33                                                                                                                                              At the instant shown, which free-body diagram best indicates the forces acting on the pendulum.   Which is larger ?  A) the weight mg or   B) the tension T?

Tension must be greater than weight 33 C. Tension must be greater than weight

34 A mass m is pulled along a rough table at constant velocity with an external force Fext at some angle above the horizontal. The magnitudes of the forces on the free-body diagram have not been drawn carefully, but the directions of the forces are correct. Which statement below must be true? Ffric > Fext , N > mg. Ffric < Fext , N < mg. Ffric > Fext , N < mg. Ffric < Fext , N > mg. None of these.

Ffric < Fext , N < mg. 34 Ffric < Fext , N < mg.

35 A mass slides down a rough inclined plane with some non-zero acceleration a1. The same mass is shoved up the same incline with a large, brief initial push. As the mass moves up the incline, its acceleration is a2. How do a1 and a2 compare? A) a1 > a2 B) a1 = a2 C) a1 < a2

35 C) a1 < a2

36 A rider in a "barrel of fun" hinds herself stuck with her back to the wall. Which diagram correctly shows the forces acting on her? A) B) C) D) E)

36 A

37 Two masses, of size m and 3m, are at rest on a frictionless surface. A compressed, massless spring between the masses is suddenly allowed to uncompress, pushing the masses apart. After the spring losses contact with both masses, the speed of m is ____ the speed of 3m. A) the same as B) twice C) three times D) four times E) none of these

37 C) three times

38 A bucket containing a brick is swung in a circle at constant speed in a vertical plane as shown. The bucket is swung fast enough that the brick does not fall out. The net force on the brick as it is swung has maximum magnitude at position Top. Bottom. Right The net force has the same magnitude at all positions.

The NORMAL force will be greatest at the bottom. 38 With constant speed, centripetal force must remain constant, therefore constant net force. The NORMAL force will be greatest at the bottom.