Exam 2--PHYS 101--Fall 2014

Transcription

1 Class: Date: Exam 2--PHYS 101--Fall 2014 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. Consider these vectors. What is A-B? a. a c. c b. b d. d 2. Consider these two vectors. What is the magnitude of their sum? Aä = 10.0 units at 30.0 degrees above the -x-axis Bä = 10.0 units along the -x-axis (Note the angle for both is measured from the negative x axis.) a units b units c units d units 3. Which of these are vector quantities? I. mass II. distance III. velocity IV. acceleration a. I b. III & IV c. I & III d. II, III, & IV e. all of these 4. A cannonball is fired horizontally at 10 m/s from a cliff. Its speed one second after being fired is about a. 16 m/s b. 10 m/s c. 14 m/s d. 20 m/s 1

2 5. A vector in the xy plane has a magnitude of 25m and an x component of 12m. The angle it makes with the positive x axis is: 8. A large cannon is fired from ground level over level ground at an angle of 30 above the horizontal. The muzzle speed is 1000 m/s. Neglecting air resistance, the projectile will travel what horizontal distance before striking the ground? a. 26 b. 241 c. 61 d. 64 e A bullet shot horizontally from a gun: a. travels in a straight line b. strikes the ground much sooner than one dropped from the same point at the same instant c. strikes the ground much later than one dropped vertically from the same point at the same instant d. strikes the ground at approximately the same time as one dropped vertically from the same point at the same instant e. never strikes the ground 7. A stone is thrown horizontally from the top of a 125-m high cliff with a velocity of 10.0m/s. How far does the stone land from the base of the cliff? a. 170 km b. 4.3 km c. 43 km d. 87 km e. 8.5 km 9. Which of these plots represents the y-component of the velocity for an object launched from the ground at an angle and returns to the same y-position? a. 10 m b. 50 m c. 5 m d. 100 m e. 200 m a. a b. b c. c d. d e. none of these 10. Given that A + B = C, and that A 2 + B 2 = C 2, how are vectors A and B oriented with respect to each other? a. separated by some unknown angle b. perpendicular c. parallel and in same direction d. separated by 30 degrees e. antiparallel (parallel but in opposite directions) 2

3 11. This figure shows the path a projectile takes when fired at an angle of 0 degrees. The dashed lines show the distance from the level of the cannon to where the projectile has fallen. The projectile travels for equal amounts of time, t, between each dashed line. If the distance M is 2 meters, what are the distances N and O? 14. A 10.0 kilogram stone is initially at rest and accelerated by a force of 15.0 newtons. After 6.0 seconds, what is the stone s velocity? a. 9.0 m/s b. 40 m/s c. 900 m/s d. 25 m/s a. N=4 m; O=8 m b. N=8 m; O=32 m c. N=2 m; O=4 m d. N=8 m; O=18 m 12. A cart is being pulled along a horizontal track by an external force and accelerating. A cannon on the cart fires straight upwards. After it is fired, what happens to the ball? a. the cannonball falls into the cart b. the cannonball falls behind the cart c. it depends on the initial velocity of the cannonball d. the cannonball falls in front of the cart 13. Which of these projectiles remains in the air for the longest amount of time? 15. You run out of gas. You and your friends have to push your car out of the road. Which of these statements best explain why it is difficult to move the car? a. the car has a big weight b. the car has a lot of mass c. the car experiences a very large frictional force d. you and your friends are very weak 16. A karate chop delivers a force of 3000 N to a board that breaks. The force that the board exerts on the hand during this event is a. less than 3000 N b N c. greater than 3000 N d. need more information 17. Consider a block that is at rest on an inclined plane. The only forces acting on the block are the frictional, normal, and gravitational forces. Which of these statements best describe the normal force acting on the block? a. N>mg b. N<mg c. N=mg d. it depends on the weight of the block a. a b. b c. c d. it depends on their initial velocity 3

4 18. You push on a mass with a certain force, and the mass accelerates at 1 m/s 2. With the same force, you push on a second mass. The acceleration of the second mass is 3 m/s 2. Now, you stick the 2 masses together and push on them with the same force. What is the acceleration of the 2 masses? 20. A block of mass 10 kg sits at rest on a horizontal surface. A force of 20 N is applied at 30 degrees from the x-axis. What is the normal force acting on the block? a. 2 m s 2 b. c. d. 1 2 m s m s m s A block of 10 kg is on an inclined plane as shown here. A rope is attached to the block and goes over a frictionless pully; a force of 100 N is applied to the rope. What is the rate of acceleration for the block? a. 80 N b. 90 N c. 10 N d. 100 N 21. For the previous problem, the coefficient of kinetic friction between the block and surface is 0.1. At what rate does the block accelerate to the right? a. 2.1 m/s 2 b. 0.8 m/s 2 c. 1.2 m/s 2 d. 1.7 m/s 2 a. 0 m/s 2 b. 1.3 m/s 2 up the inclined plane c. 3.2 m/s 2 up the inclined plane d. 2.0 m/s 2 down the inclined plane e. 5.0 m/s 2 up the inclined plane 4

5 22. We step on the accelerator of our Subaru providing a force F on the car for a time of 10 seconds and speeding it up to a final speed of 60 miles/hour. If the applied force were 1 F, what would be the final 2 speed after 20 seconds? 25. The normal force on an object is always: a. equal to the gravitational force b. abnormally large c. in the upward direction d. perpendicular to the surface on which the object sits e. opposite the direction of the object s motion 26. Which of these statements about the coefficients of friction is true? a. 90 miles/hour b. 30 miles/hour c. 120 miles/hour d. 60 miles/hour 23. A cart is on a horizontal frictionless table. Once the cart has been pushed and released, what will happen to it? a. it will immediately come to a stop b. it will continue at constant velocity c. it will continue at constant acceleration d. it will gradually slow down a. µ s >µ k b. µ s <µ k c. µ s =µ k 27. You apply a force in the x-direction of 20 N on a block that has a mass of 10 kg. If no other forces act on the block, what is its acceleration? a. 2 m/s 2 b. 200 m/s 2 c. 0.5m/s 2 d. 5 m/s An elevator goes downward at a constant acceleration. What is the relationship between the weight of the object (W) and the normal force on the block (N)? a. W>N b. W=N c. W<N d. not enough information 5

6 Exam 2--PHYS 101--Fall 2014 Answer Section MULTIPLE CHOICE 1. ANS: A PTS: 1 2. ANS: B PTS: 1 3. ANS: B PTS: 1 4. ANS: C PTS: 1 5. ANS: C PTS: 1 6. ANS: D PTS: 1 7. ANS: B PTS: 1 8. ANS: D PTS: 1 9. ANS: E PTS: ANS: B PTS: ANS: D PTS: ANS: B PTS: ANS: A PTS: ANS: A PTS: ANS: B PTS: ANS: B PTS: ANS: B PTS: ANS: D PTS: ANS: E PTS: ANS: B PTS: ANS: B PTS: ANS: D PTS: ANS: B PTS: ANS: A PTS: ANS: D PTS: ANS: A PTS: ANS: A PTS: 1 1