Review Problems for Physics A Final

Transcription

1 Review Problems for Physics A Final 1. The fastest helicopter, the Westland Lynx, can travel 3.33 km in the forward direction in just 30.0 s.what is the average velocity of this helicopter? Express your answer in both meters per second and kilometers per hour. 111 m/s, 400km/hr 2. Eustace drives 20.0 km to the east when he realizes he left his wallet at home. He drives 20.0 km west to his house, takes 5.0 min to find his wallet, then leaves again. Eustace is 40.0 km east of his house exactly 60.0 min after he left the first time. a.what is his average velocity? 40 km/hr b.what is his average speed? 80 km/hr 3. A minivan travels along a straight road. It initially starts moving toward the east. Below is the position-time graph of the minivan. Use the information in the graph to answer the questions. 1. Does the minivan move to the east? If so, during which time interval(s)? 10-40, Does the minivan move to the west? If so, during which time interval(s)? Is the minivan s speed between t 1 and t 2 greater than, less than, or equal to its speed between t 2 and t 3? Greater than. 4. Is the minivan s speed between t 4 and t 5 greater than, less than, or equal to its speed between t 6 and t 7? Greater than. 5. Does the minivan ever stop completely? If so, at which time(s)? 0-10, Does the minivan ever move with a constant velocity? If so, at which time(s)?

2 10-20, 20-40, 40-50, What is the total displacement of the minivan during the trip? -5m 4. Read the book. It will help you with concepts. 5. A gumdrop is released from rest at the top of the Empire State Building, which is 381 m tall. Disregarding air resistance, calculate the displacement of the gumdrop after 1.00, 2.00, and 3.00 s. 4.9m, 19.6m, 44.1m 6. A small sandbag is dropped from rest from a hovering hot-air balloon. After 2.0 s, how far below the balloon is the sand bag? 19.6m 7. A physics student throws a softball straight up into the air with a speed of 17.5 m/s. The ball is in the air for a total of 3.60 s before it is caught at its original position. How high does the ball rise? m 8. A surface probe lands on a highland region of the planet Mercury. A few hours later the ground beneath the probe gives way and the probe falls, landing below its original position with a velocity of 11.2 m/s downward. If the free-fall acceleration near Mercury s surface is 3.70 m/s2 downward, what is the probe s displacement? m 9. A ball thrown vertically is caught by the thrower after 5.1 s. Find the maximum height the ball reaches m 10. Find the initial velocity with which the ball in problem 6 is thrown m/s 11. An archer fires an arrow directly upward, then quickly runs from the launching spot to avoid being struck by the returning arrow. If the arrow s initial velocity is 85.1 m/s upward how long does the archer have to run away before the arrow lands? 17.37s 12. A popular scene in recent action films shows a character in free-fall speed up to catch a freely falling parachute. Suppose a packed parachute is dropped from rest from an airplane and that a daredevil is launched straight down from the plane 3.00 s later. Neglecting air resistance, the daredevil catches up to the parachute 4.00 s after the daredevil leaves the plane. What are the daredevil s initial and final velocities? Initial = 40.4m/s, Final = 79.6m/s

3 13. The elevators in the Landmark Tower in Yokohama, Japan, are among the fastest in the world. They accelerate upward at m/s2 for 4.00 s to reach their maximum speed. Suppose an empty elevator is moving upward with its maximum speed when the cable breaks, so that the elevator slows down, comes to a stop, and then begins to fall freely. What will the elevator s velocity be 0.00 s, 1.00 s, 2.00 s, and 3.00 s after the cable breaks? 12.5m/s, 2.7m/s, -7.1m/s, -16.9m/s 16. A thoroughbred racehorse accelerates uniformly at 7.56 m/s2, reaching its final speed after running 19.0 m. If the horse starts at rest, what is its final speed? m/s 17. A soccer ball moving with an initial speed of 1.8 m/s is kicked with a uniform acceleration of 6.1 m/s2, so that the ball s new speed is 9.4 m/s. How far has the soccer ball moved? 6.9m 18. A dog runs with an initial velocity of 1.50 m/s to the right on a waxed floor. It slides to a final velocity of 0.30 m/s to the right with a uniform acceleration of 0.35 m/s2 to the left. What is the dog s displacement? 3.09m 19. A hippopotamus can run up to 30 km/h, or 8.33 m/s. Suppose a hippopotamus uniformly accelerates m/s2 until it reaches a top speed of 8.33 m/s. If the hippopotamus has run 46.3 m, what is its initial speed? 2.57 m/s 20. A toy parachute is dropped from an open window that is 13.0 m above the ground. If the parachute travels 9.0 m horizontally, what is the resultant displacement? 15.8m, 55 below horizontal 21. The Palm Springs Aerial Tramway extends 3.88 km from the Valley Station, which is located 0.8 km above sea level, to the Mountain Station atop San Jacinto Peak. The actual path of the tramway s cables is not along a straight line, but if it were, the

4 horizontal displacement of the tramway would be 3.45 km. How far is San Jacinto Peak above sea level? 2.57m 22. U.S. Highway 212 extends 55 km at 37 north of east between Newell and Mud Butte, South Dakota. It then continues for 66 km nearly due east from Mud Butte to Faith, South Dakota. If you drive along this part of U.S. Highway 212, what will be your total displacement? 114km, 16.9 N of E 23. An Arctic tern flying to Antarctica encounters a storm. The tern changes direction to fly around the storm. If the tern flies 46 km at 15 south of east, 22 km at 13 east of south, and finally 14 km at 14 west of south, what is the tern s resultant displacement? 65km 45.6 S of E 24. In 1977, a helicopter at the heliport atop the 59-story Pan Am building in New York fell over, causing the rapidly-turning rotor blades to splinter. One of these fragments landed about 101 m away, near the corner of Madison Avenue and 43rd Street. Suppose the fragment moved off the building horizontally with a speed of m/s. Use this information to find the height of the Pan Am building m 25. A lunch pail is accidentally kicked off a steel beam on a building under construction. Suppose the initial horizontal speed is 1.50 m/s. How far does the lunch pail fall after it travels 3.50 m horizontally? 26.7m 26. A baseball is thrown with an initial speed of 15.0 m/s. If the ball s horizontal displacement is 17.6 m, at what angle with respect to the ground is the ball pitched? A shingle slides down a roof having a 30.0 pitch and falls off with a speed of 2.0 m/s. How long will it take to hit the ground 45 m below? 2.93s

5 28. A ball is thrown from a roof with a speed of 10.0 m/s and an angle of 37.0 with respect to the horizontal. What are the vertical and horizontal components of the ball s displacement 2.5 s after it is thrown? Horizontal 20m, Vertical m 29. A bird flies directly into a wind. If the bird s forward speed relative to the wind is 58.0 km/h and the wind s speed in the opposite direction is 55.0 km/h, relative to Earth, how long will it take the bird to fly 1.4 km?.467 hr 30. An airship moving north at 55.0 km/h with respect to the air encounters a wind from 17.0 north of west. If the wind s speed with respect to Earth is 40.0 km/h, what is the airship s velocity with respect to Earth? km/hr, 41.5 N of E 31. A sailboat travels south with a speed of 12.0 km/h with respect to the water. Suppose the boat encounters a current that has a velocity with respect to Earth of 4.0 km/h at 15.0 south of east. What is the sailboat s resultant velocity with respect to Earth? 13.59km/hr, 73 S of E 32. Three workers move a car by pulling on three ropes. The first worker exerts a force of N to the north, the second a force of N to the east, and the third N at 30.0 south of east. In what precise direction does the car move? 1360N, N of E 33. A shopper pushes a grocery cart by exerting a force on the handle. If the force equals 76 N at an angle of 40.0 below the horizontal, how much force is pushing the cart in the forward direction? What is the component of force pushing the cart against the floor? 58.21N, 48.85N 34. A traffic signal is supported by two cables, each of which makes an angle of 40.0 with the vertical. If each cable can exert a maximum force of 102 N, what is the largest weight they can support? N

6 35. Suppose an empty grocery cart rolls downhill in a parking lot. The cart undergoes a constant increase in speed of 1.0 m/s over a 5.0 s interval. If the downhill force acting on the cart is 18.0 N and the uphill force due to friction is 15.0 N, what is the cart s mass? 15kg 36. A 214 kg boat is sinking in the ocean. The boat s weight is partially offset by the 790 N buoyant force of the water. What is the net acceleration of the boat? 6.1 m/s A 90.0 kg skier glides down a slope with an incline of 17.0.What frictional force is needed for the skier to move at a constant velocity? 257.9N 38. A snowboarder slides down a 5.0 slope at a constant speed. What is the coefficient of kinetic friction between the snow and the board? A 25 kg box is pushed across a floor. The coefficients of friction are 0.9 and 0.65 for static and kinetic. How much force is required to break it loose and what is the acceleration of the box after it is sliding? 220N, 2.45m/s A building under construction requires building materials to be raised to the upper floors by cranes or elevators. An amount of cement is lifted 76.2 m by a crane, which exerts a force on the cement that is slightly larger than the weight of the cement. If the net work done on the cement is J, what is the magnitude of the net force exerted on the cement? 17.19N 41. A car has run out of gas. Fortunately, there is a gas station nearby. You must exert a force of 715 N on the car in order to move it. By the time you reach the station, you have done J of work. How far have you pushed the car? 38N 42. A 50.0 kg parachutist falls at a speed of m/s when the parachute opens. The parachutist s speed upon landing is 5.00 m/s.

7 How much work is done by the air to reduce the parachutist s speed? 54,600J 43. A 5.0 kg stone is slid up a frictionless ramp that has an incline of How long is the ramp if the gravitational potential energy associated with the stone is J? 11.59m 44. What would be the kinetic energy of a g raindrop if it fell km without any resistance provided by air? 1.225J 45. A toy rocket is at a height of 75.0 m and is moving upward with a speed of 1.2 m/s when it ejects a payload with a mass of 20.0 g. The payload has an initial upward speed relative to the rocket of 3.5 m/s. What is the height reached by the payload when its upward velocity is zero? 76.13m 46. A g arrow is pulled back 30.0 cm against a bowstring. If the spring constant of the bowstring is 1250 N/m, at what speed will the arrow leave the bow? m/s 47 If you were to neglect air resistance, a projectile fired straight up into the air would land again with the speed with which it was fired. (This is why it is dangerous to shoot a bullet directly upward.) However, some of the energy is lost because of air resistance. Suppose a 50.0 g projectile is fired upward with an initial speed of m/s. If it lands with a speed of 89.0 m/s, how much mechanical energy is given up because of air resistance? J 48. Although it cannot sustain its top speed for more than 8.65 s, the cheetah can run a distance of 274 m during that time. If a cheetah with a mass of 50.0 kg is moving north at its top speed, what is its momentum? kgm/s 49. A net force of 10.0 N to the right pushes a 3.0 kg book across a table. If the force acts on the book for 5.0 s, what is the book s final velocity? Assume the book to be initially at rest m/s

8 50. How much time would it take for a 0.17 kg ice hockey puck to decrease its speed by 9.0 m/s if the coefficient of kinetic friction between the ice and the puck is 0.050? 18.38s 51. A 63 kg astronaut drifting with 7.0 m/s to the right with respect to a spacecraft uses a jet pack to slow down. If it takes 14.0 s to come to a stop with respect to the spacecraft, what is the force exerted by the jet pack? How far does the astronaut travel before stopping? 31.5N, 49m 52. A 0.5 kg tetherball is traveling at 3 m/s when struck in the opposite direction for 0.3 s. It is now traveling at 5 m/s back the way it came. What was the force of the blow? 13.33N 53. A 1550 kg torpedo strikes a 770 kg target that is initially at rest. If the combined torpedo and target move forward with a speed of 9.44 m/s, what is the initial velocity of the torpedo? Assume that no resistance is provided by the water m/s 54. A railway car with a mass of 8500 kg and a velocity of 4.5 m/s to the right collides inelastically with a railway car with a mass of 9800 kg and a velocity of 3.9 m/s to the left. What is the final velocity of the combined cars? Two flying fish have an inelastic collision while in mid-flight. One fish has a mass of kg and a velocity of 15.0 m/s to the right; the other has a mass of kg and a velocity of 13.5 m/s to the left. Find the change in their kinetic energy after the collision J