Physics 20 Practice Problems for Exam 1 Fall 2014

Transcription

1 Physics 20 Practice Problems for Exam 1 Fall 2014 Multiple Choice Short Questions (1 pt ea.) Circle the best answer. 1. An apple falls from a tree and hits the ground 5 meters below. It hits the ground with a speed of about a) 5 m/s b) 10 m/s c) 15m/s d) 20 m/s 2. Disregarding air drag, how fast must you toss a ball straight up in order for it to take 2 seconds to return to the level from which you tossed it? a) 5 m/s b) 7.5 m/s c) 10 m/s d) 15 m/s e) 20 m/s 3. When a rock thrown straight upwards gets to the exact top of its path, its a) velocity is zero and its acceleration is zero. b) velocity is zero and its acceleration is about 10 meters per second per second. c) velocity is about 10 m/s and its acceleration is zero. d) velocity is about 10 m/s and its acceleration is about 10 meters per second per second. 4. Someone standing at the edge of a cliff throws one ball straight up and another ball straight down at the same initial speed. Neglecting air resistance, the ball to hit the ground below the cliff with the greater speed will be a) the one thrown upward. b) the one thrown downward c) they will both ht with the same speed. 5. The number has how many significant figures? a. 2 b. 3 c. 5 d A push of magnitude P acts on a box of weight W as shown in the figure. The push is directed at an angle θ below the horizontal, and the box remains a rest. The box rests on a horizontal surface that has some friction with the box. The normal force on the box due to the floor is equal to A) W. B) W + P. C) W + P cos θ. D) W + P sin θ. E) W - P sin θ. 7. When a car goes around a circular curve on a horizontal road at constant speed, what force causes it to follow the circular path? A) the normal force from the road B) the friction force from the road C) gravity D) Magic 8. In order to get an object moving, you must push harder on it than it pushes back on you. A) True B) False 9. When a car goes around a banked circular curve at the proper speed speed for the banking angle, what force cause it to follow the circular path? A) the normal force from the road B) the friction force from the road C) gravity D) Magic 10. If you swing a bucket of water fast enough in a vertical circle, at the highest point the water does not spill out. This happens because an outward force balances the pull of gravity on the water. A) True B) False

2 Problems Show all work for any credit. Box final answers. Circle the Best Answer. Neatness Counts. 1. A motorist travels for 3.0 h at 80 km/h and 2.0 h at 100 km/h. What is her average speed for the trip? A) 85 km/h B) 88 km/h C) 90 km/h D) 92 km/h 2. A cart with an initial velocity of 5.0 m/s to the right experiences a constant acceleration of 2.0 m/s2 to the right. What is the cart's displacement during the first 6.0 s of this motion? A) 10 m B) 55 m C) 66 m D) 80 m 3. A ball is thrown straight up with a speed of 36 m/s. How long does it take to return to its starting point, assuming negligible air resistance? A) 3.7 s B) 7.3 s C) 11 s D) 15 s 4. You walk 53 m to the north, then you turn 60 to your right and walk another Determine the direction of your displacement vector. Express your answer as an angle relative to east. Sketch it. A) 63 N of E B) 50 N of E C) 57 N of E D) 69 N of E

3 5. Vector has a magnitude of 6.0 m and points 30 north of east. Vector has a magnitude of 4.0 m and points 30 west of north. Sketch it. The resultant vector + is given by A) 9.8 m at an angle of 64 east of north. B) 9.8 m at an angle of 26 north of east. C) 7.2 m at an angle of 26 east of north. D) 3.3 m at an angle of 26 north of east. E) 3.3 m at an angle of 64 east of north. 6 A stone is thrown horizontally with an initial speed of 10 m/s from the edge of a cliff. A stopwatch measures the stone's trajectory time from the top of the cliff to the bottom to be 4.3 s. What is the height of the cliff if air resistance is negligibly small? A) 22 m B) 43 m C) 77 m D) 91 m

4 7. A 6.00-kg ornament is held at rest by two light wires that form 30 angles with the vertical, as shown in the figure. An external force of magnitude F acts vertically downward on the ornament. The tension exerted by each of the two wires is denoted by T. A free-body diagram, showing the four forces that act on the box, is shown in the figure. If the magnitude of force F is 410 N, what is the magnitude of the tension T? A) 271 N B) 235 N C) 188 N D) 376 N E) 470 N 8. A 6.0-kg box slides down an inclined plane that makes an angle of 39 with the horizontal. If the coefficient of kinetic friction is 0.40, at what rate does the box accelerate down the slope? A) 3.1 m/s2 B) 3.4 m/s2 C) 3.7 m/s2 D) 4.1 m/s2

5 9. A car moving at a steady 10 m/s on a level highway encounters a bump that has a circular cross-section with a radius of 30 m. The car maintains its speed over the bump. What is the normal force exerted by the seat of the car on a 60.0-kg passenger when the car is at the top of the bump? A) 200 N B) 390 N C) 790 N D) 490 N E) 590 N 10. The curved section of a speedway is a circular arc having a radius of 190 m. This curve is properly banked for racecars moving at 34 m/s. At what angle with the horizontal is the curved part of the speedway banked? A) 32 B) 34 C) 30 D) 28 E) A roller-coaster car has a mass of 500 kg when fully loaded with passengers. At the bottom of a circular dip of radius 40 m (as shown in the figure) the car has a speed of 16 m/s. What is the magnitude of the force of the track on the car at the bottom of the dip? a. 3.2 kn b. 8.1 kn c. 4.9 kn d. 1.7 kn e. 5.3 kn