Physics 1A (Rappel) Fall 2011: Final Version a 3

Physics 1A (Rappel) Fall 2011: Final Version A 1 No work needs to be shown for multiple-choice questions. g=9.8 m/s2

1. A ladder rest against a smooth frictionless wall and makes an angle of  with the horizontal. The coefficient of static friction between the ladder and the ground is 0.2. What is the minimum angle  such that the ladder does not slip? d. 68.20.

2. A vertical spring with a spring constant of 100 N/m is compressed by 10 cm. A ball with a mass of 0.1 kg is placed on top of this compressed spring. When the spring is released, how far does the ball shoot up in the air (note: this is the distance calculated from the original, compressed position)? b. 0.51 m.

3. A canon with a mass of 100 kg is resting on ice (a frictionless surface). When it fires a 1 kg canonball in the horizontal direction, the canon’s velocity is measured as 1 m/s with respect to the ice. What is the velocity of the canonball with respect to the ice? e. 100 m/s in the direction opposite to the velocity of the canon. 5. Two blocks, with a mass of 20kg and 10kg respectively, are connected by a string that passes over a pulley as shown. There is no slipping between the string and the pulley has a radius of R and a mass of 2 kg. The pulley has a 2 moment of inertia of 0.5MR . The acceleration of m2 is:? a. 3.2 m/s2.

6. A red ball is projected horizontally from the roof of a tall building. Another ball, identical to the red ball except that it is blue, is released from the same roof at the same instant. Ignoring air resistance: a. both balls land at the same instant but the red ball has more speed.

7. A soccer ball, initially at rest and with a mass of 0.5 kg, is kicked with a speed of 20 m/s. The ball lands 40 m away from the point where it was kicked. What was the angle with the horizontal with which it was kicked?

e. 39.30.

8. A billiard ball collides elastically with another billiard ball (with identical mass) that is initially at rest. The velocity of the first ball after the collision is measured as (0.5 m/s) i+(0.5 m/s) j while the velocity of the second ball is measured as (0.5 m/s) i-(0.5 m/s) j. The velocity of the first ball before the collision could be given by: b. (1.0 m/s) i+0 j

10.07.11 Physics 1A (Rappel) Fall 2011: Final Version A 2 9. A 10 kg book is dropped onto the floor from a height of 1 m. The magnitude of the momentum of the book just before the collision is: b. 44.3 kgm/s.

10. A 100 N force is applied on a rod of length 1m as shown in the figure. The magnitude of the torque produced by the force about the pivot point O is: e. 37.5 Nm.

11. A 1 kg mass is spun in a circular motion in the vertical plane with a 1m long rope. The angular velocity of the mass is 1 rad/s. What is the tension in the rope at the lowest point of its path? c. 10.8 N.

12. A raindrop with a mass of 10 g falls through the sky with a constant velocity of 2 m/s. What is the work done by air friction during 1 second? d. -0.196 N.

13. A stone is thrown from a 30 m high building straight up into the air. If the initial velocity is 5 m/s, how long does it take for the stone to hit the ground? a. 3.04 s. 14. A block with a weight of 100N is placed on a horizontal table. The coefficient of static friction between the block and the table is 0.2. A horizontal force is applied to the block. At what force is the block about the “break loose” and start moving? c. 20 N.

15. A bird is flying horizontally and drops a berry from a height of 10 m. When the berry hits the ground, its velocity vector makes an angle of -400 with the horizontal. What is the speed of the bird when it dropped the berry? b. 16.7 m/s.

16. A figure skater is spinning around her length axis with an angular velocity of 2 rad/s with her arms extended. She then pulls her arms inwards, changing her moment of inertia from 3 kgm2 to 1 kgm2. What will be her angular velocity after she has pulled in her arms? c. 6 rad/s. 17. A block is pulled along a horizontal surface with a constant velocity of 2m/s. If the pulling force is 100 N then what is the power output of the friction force? d. 200 W. 18. Two cars, traveling at equal speed, collide head on, resulting in a perfectly inelastic collision. The mass of the second car is twice that of the first car. What can you say about the velocity of the cars immediately after the collision? e. The velocity of the cars is equal to one-third the velocity of the second car before the collision.

10.07.11 Physics 1A (Rappel) Fall 2011: Final Version A 3 19. At t=0s a car is traveling at a certain velocity, when it begins to slow down at a rate of -2 m/s2. After 10s it has traveled 210 m. Its original velocity was: e. 31 m/s.

20. A 3 kg picture is hung from a wire as shown. The tension in the wire is 60 N. The angle  is:

e. 14.20.  

21. A 10 kg block is placed on a 580 incline. The coefficient of static friction between the block and the incline is 0.15 and the coefficient of kinetic friction is 0.1. What will the acceleration of the block be? a. 7.8 m2/s.

22. A basketball floats in a bathtub of water. The ball has a mass of 0.5 kg and a diameter of 22 cm. What is the buoyant force? c. 4.9 N.

23. A research submarine has a 20.0 cm-radius round window. The manufacturer says that the window can withstand forces up to 1.20×106 N. What is the submarine's maximum safe depth (assume that the pressure inside the submarine is equal to the pressure at the water’s surface and that the density of water 1s 1000 kg/m3)? d. 974 m.

24. A 2kg block is attached to a massless string that is wrapped around a cylinder with a radius of 1m and a mass of 4kg. The block is released from rest. What is the kinetic energy of the cylinder when the block has fallen over a distance of 1m (the moment of inertia of a cylinder is I=0.5MR2 and there is no slipping between the string and the cylinder)? a. 9.8 J.

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