Physics 1401 - Exam 2 Chapter 5N-New

1 Physics 1401 - Exam 2. Chapter 5N-New 2. The second hand on a watch has a length of mm and makes one revolution in s. What is the speed of the end of the second hand as it moves in uniform circular motion? (a) 10-4 m/s (c) 10-3 m/s (e) 10-5 m/s (b) 10-3 m/s (d) 10-4 m/s 3. Approximately one billion years ago, the Moon orbited the Earth much closer than it does today. The radius of the orbit was only 24 400 km. Today, the radius is 385 000 km. The orbital period was only 23 400 s. The present period is 106 s. Assume that the orbit of the Moon is circular. Calculate the ratio of the speed of the Moon in its ancient orbit to the speed that it has today. (a) (c) (e) (b) (d) 5. A ball is whirled on the end of a string in a horizontal circle of radius R at constant speed v. The centripetal acceleration of the ball can be increased by a factor of 4 by (a) keeping the speed fixed and increasing the radius by a factor of 4. (b) keeping the radius fixed and increasing the speed by a factor of 4.

2 (c) keeping the radius fixed and increasing the period by a factor of 4. (d) keeping the radius fixed and decreasing the period by a factor of 4. (e) keeping the speed fixed and decreasing the radius by a factor of 4. 7. A car traveling at 20 m/s rounds a curve so that its centripetal acceleration is 5 m/s2. What is the radius of the curve? (a) 4 m (c) 80 m (e) 640 m (b) 8 m (d) 160 m Review Exam -1- 8. A satellite is placed in a circular orbit to observe the surface of Mars from an altitude of 144 km. The equatorial radius of Mars is 3397 km. If the speed of the satellite is 3480. m/s, what is the magnitude of the centripetal acceleration of the satellite? (a) m/s2 (c) m/s2 (e) m/s2. (b) m/s2 (d) m/s2. 11. A boy is whirling a stone around his head by means of a string. The string makes one complete revolution every second, and the tension in the string is FT. The boy then speeds up the stone, keeping the radius of the circle unchanged, so that the string makes two complete revolutions every second.

3 What happens to the tension in the sting? (a) The tension is unchanged. (b) The tension reduces to half of its original value. (c) The tension increases to twice its original value. (d) The tension increases to four times its original value. (e) The tension reduces to one-fourth of its original value. 14. Sara puts a box into the trunk of her car. Later, she drives around an unbanked curve that has a radius of 48 m. The speed of the car on the curve is 16 m/s, but the box remains stationary relative to the floor of the trunk. Determine the minimum coefficient of static friction for the box on the floor of the trunk. (a) (d) (b) (e) This cannot be determined without knowing the mass of (c) the box. 15. In an amusement park ride , a small child stands against the wall of a cylindrical room that is then made to rotate. The floor drops downward and the child remains pinned against the wall. If the radius of the device is m and the relevant coefficient of friction between the child and the wall is , with what minimum speed is the child moving if he is to remain pinned against the wall?

4 (a) m/s (c) m/s (e) m/s (b) m/s (d) m/s Review Exam -2- 18. The maximum speed at which a car can safely negotiate an unbanked curve depends on all of the following factors except (a) the diameter of the curve. (b) the acceleration due to gravity. (c) the coefficient of static friction between the road and the tires. (d) the coefficient of kinetic friction between the road and the tires. (e) the ratio of the static frictional force between the road and the tires and the normal force exerted on the car. 20. Determine the minimum angle at which a roadbed should be banked so that a car traveling at m/s can safely negotiate the curve if the radius of the curve is 102 m. (a) (c) (e) . (b) (d) . Questions 23 through 25 pertain to the statement below: A 1000-kg car travels along a straight 500-m portion of highway (from A to B) at a constant speed of 10 m/s. At B, the car encounters an unbanked curve of radius 50 m. The car follows the road from B to C traveling at a constant speed of 10 m/s while the direction of the car changes from east to south.

5 23. What is the magnitude of the acceleration of the car as it travels from A to B? (a) 2 m/s2 (c) 10 m/s2 (e) zero m/s2. 2 2. (b) 5 m/s (d) 20 m/s 24. What is the magnitude of the acceleration of the car as it travels from B to C? (a) 2 m/s2 (c) 10 m/s2 (e) zero m/s2. (b) 5 m/s2 (d) 20 m/s2. 25. What is the magnitude of the frictional force between the tires and the road as the car negotiates the curve from B to C? (a) 20 000 N (c) 5000 N (e) 1000 N. (b) 10 000 N (d) 2000 N. Review Exam -3- 26. The earth exerts the necessary centripetal force on an orbiting satellite to keep it moving in a circle at constant speed. Which statement best explains why the speed of the satellite does not change although there is a net force exerted on it? (a) The satellite is in equilibrium. (b) The acceleration of the satellite is zero m/s2. (c) The centripetal force has magnitude mv2/r. (d) The centripetal force is canceled by the reaction force.

6 (e) The centripetal force is always perpendicular to the velocity. 30. A satellite is placed in equatorial orbit above Mars, which has a radius of 3397 km and a mass MM = 1023 kg. The mission of the satellite is to observe the Martian climate from an altitude of 488 km. What is the orbital period of the satellite? (a) 102 s (c) 103 s (e) 1012 s (b) 103 s d) 105 s 45. A 25-kg box is sliding down an ice-covered hill. When it reaches point A, the box is moving at 11 m/s. Point A is at the bottom of a circular arc that has a radius R = m. What is the magnitude of the normal force on the box at Point A? (a) 250 N (d) 650 N. (b) 280 N (e) 900 N. (c) 400 N. Review Exam -4- Questions 49 through 52 pertain to the situation described below: A 1500-kg car travels at a constant speed of 22 m/s around a circular track that has a radius of 85 m. 49. Which statement is true concerning this car? (a) The velocity of the car is changing.

7 (b) The car is characterized by constant velocity. (c) The car is characterized by constant acceleration. (d) The car has a velocity vector that points along the radius of the circle. (e) The car has an acceleration vector that is tangent to the circle at all times. 50. What is the magnitude of the acceleration of the car? (a) m/s2 (c) m/s2 (e) zero m/s2. (b) m/s2 (d) m/s2. 51. What is the average velocity of the car during one revolution? (a) m/s (c) 26 m/s (e) zero m/s (b) 12 m/s (d) 44 m/s 52. Determine the magnitude of the net force that acts on the car. (a) 390 N (c) 103 N (e) zero newtons 4. (b) 1800 N (d) 10 N. 53. Jupiter has a mass that is roughly 320 times that of the Earth and a radius equal to 11. times that of the Earth. What is the acceleration due to gravity on the surface of Jupiter? (a) m/s2 (c) 26 m/s2 (e) 260 m/s2. 2 2. (b) m/s (d) 87 m/s Review Exam -5- Physics 1401. Chapter 6 Review - Energy 1. In which one of the following situations is zero net work done?

8 (a) A ball rolls down an inclined plane. (b) A Physics student stretches a spring. (c) A projectile falls toward the surface of Earth. (d) A box is pulled across a rough floor at constant velocity. (e) A child pulls a wagon across a rough surface causing it to accelerate. 3. A concrete block is pulled m across a frictionless surface by means of a rope. The tension in the rope is 40 N; and the net work done on the block is 247 J. What angle does the rope make with the horizontal? (a) 28 (c) 47 (e) 88 . (b) 41 (d) 62 . 6. A force of magnitude 25 N directed at an angle of 37 above the horizontal moves a 10- kg crate along a horizontal surface at constant velocity. How much work is done by this force in moving the crate a distance of 15 m? (a) zero joules (c) 40 J (e) 300 J. (b) J (d) 98 J. Review Exam -6- 7. A constant force of 25 N is applied as shown to a block which undergoes a displacement of m to the right along a frictionless surface while the force acts.

9 What is the work done by the force? (a) zero joules (c) 94 J (e) 160 J. (b) +94 J (d) +160 J. 11. Which one of the following statements concerning kinetic energy is true? (a) It can be measured in watts. (b) It is always equal to the potential energy. (c) It is always positive. (d) It is a quantitative measure of inertia. (e) It is directly proportional to velocity. 15. The kinetic energy of a car is 8 106 J as it travels along a horizontal road. How much work is required to stop the car in 10 s? (a) zero joules (c) 8 105 J (e) 8 107 J. 4 6. (b) 8 10 J (d) 8 10 J. Review Exam -7- 18. A bullet traveling horizontally at 755 m/s strikes a stationary target and stops after penetrating cm into the target. What is the average force of the target on the bullet? (a) 104 N (c) 103 N (e) 104 N. 5 4. (b) 10 N (d) 10 N. 22. An elevator supported by a single cable descends a shaft at a constant speed. The only forces acting on the elevator are the tension in the cable and the gravitational force.

10 Which one of the following statements is true? (a) The magnitude of the work done by the tension force is larger than that done by the gravitational force. (b) The magnitude of the work done by the gravitational force is larger than that done by the tension force. (c) The work done by the tension force is zero joules. (d) The work done by the gravitational force is zero joules. (e) The net work done by the two forces is zero joules. 24. A 1500-kg elevator moves upward with constant speed through a vertical distance of 25. m. How much work was done by the tension in the cable? (a) 990 J (c) 140 000 J (e) 430 000 J. (b) 8100 J (d) 370 000 J. Review Exam -8- 26. Two balls of equal size are dropped from the same height from the roof of a building. One ball has twice the mass of the other. When the balls reach the ground, how do the kinetic energies of the two balls compare? (a) The lighter one has one fourth as much kinetic energy as the other does.