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Chapter 3 Pretest
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1. After a body has fallen freely from rest for 8.0 s, its velocity is approximately: A) 40 m/s downward, B) 80 m/s downward, C) 120 m/s downward, D) 160 m/s downward.
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1. After a body has fallen freely from rest for 8.0 s, its velocity is approximately: A) 40 m/s downward, B) 80 m/s downward, C) 120 m/s downward,
D) 160 m/s downward.
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2. The body in item 1 fell approximately: A) 40 m, B) 80 m, C) 160 m, D) 320 m.
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2. The body in item 1 fell approximately: A) 40 m, B) 80 m, C) 160 m, D) 320 m.
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3. An object is accelerated from rest at the rate of 3.0 m/s2. After it has traveled13.5 m, its velocity is: A) 3.0 m/s, B) 6.0 m/s, C) 9.0 m/s, D) 12.0 m/s.
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3. An object is accelerated from rest at the rate of 3.0 m/s2. After it has traveled13.5 m, its velocity is: A) 3.0 m/s, B) 6.0 m/s, C) 9.0 m/s, D) 12.0 m/s.
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4. Which of the following is a physical quantity that has both magnitude and direction?a. vector b. scalarc. resultantd. frame of reference
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4. Which of the following is a physical quantity that has both magnitude and direction?a. vector b. scalarc. resultantd. frame of reference
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5. A string attached to an airborne kite was maintained at an angle of 40.0° with the ground. If 120 m of string was reeled in to return the kite back to the ground, what was the horizontal displacement of the kite?a. 110 m b. 84 mc. 77 m d. 92 m
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5. A string attached to an airborne kite was maintained at an angle of 40.0° with the ground. If 120 m of string was reeled in to return the kite back to the ground, what was the horizontal displacement of the kite?a. 110 m b. 84 mc. 77 m d. 92 m
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6. Which of the following is the motion of objects moving in two dimensions under the influence of gravity?a. horizontal velocityb. directrixc. parabolad. projectile motion
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6. Which of the following is the motion of objects moving in two dimensions under the influence of gravity?a. horizontal velocityb. directrixc. parabolad. projectile motion
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7. What is the path of a projectile?a. a wavy lineb. a parabolac. a hyperbolad. Projectiles do not follow a predictable path.
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7. What is the path of a projectile?a. a wavy lineb. a parabolac. a hyperbolad. Projectiles do not follow a predictable path.
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8. A piece of chalk is dropped by a teacher walking at a speed of 1.5 m/s. From the teacher’s perspective, the chalk appears to fall:a. straight down b. straight down and backward c. straight down and forward d. straight backward
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8. A piece of chalk is dropped by a teacher walking at a speed of 1.5 m/s. From the teacher’s perspective, the chalk appears to fall:a. straight down b. straight down and backward c. straight down and forward d. straight backward
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9. A person rows directly westward across a stream that flows southward. The person can row the boat in still water at a greater speed than the rate of flow of the stream. The direction of the resultant velocity of the boat is: A) west, B) between west and southwest, C) between southwest and south, D) south.
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9. A person rows directly westward across a stream that flows southward. The person can row the boat in still water at a greater speed than the rate of flow of the stream. The direction of the resultant velocity of the boat is: A) west, B) between west and southwest, C) between southwest and south, D) south.
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10. If, in item 1, the person can row the boat at 6.0 km/h and the stream flows at 3.0 km/h, the magnitude of the resultant velocity is: A) less than 3.0 km/h, B) between 3.0 km/h and 6.0 km/h, C) between 6.0 km/h and 9.0 km/h, D) greater than 9.0 km/h.
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10. If, in item 1, the person can row the boat at 6.0 km/h and the stream flows at 3.0 km/h, the magnitude of the resultant velocity is: A) less than 3.0 km/h, B) between 3.0 km/h and 6.0 km/h, C) between 6.0 km/h and 9.0 km/h, D) greater than 9.0 km/h.
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11. A vector is a quantity that has:A) magnitude and direction. B) time and direction. C) magnitude and time.
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11. A vector is a quantity that has:A) magnitude and direction. B) time and direction. C) magnitude and time.
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12. The horizontal component of a projectile’s velocity is independent of:A) the vertical component of its velocity. B) time. C) the range of the projectile.
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12. The horizontal component of a projectile’s velocity is independent of:A) the vertical component of its velocity. B) time. C) the range of the projectile.
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13. A ball thrown in the air will never go as far as physics ideally would predict because:A) gravity is acting. B) one can never throw the ball fast enough. C) ideally the ball would never land. D) air friction slows the ball. E) all of the above.
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13. A ball thrown in the air will never go as far as physics ideally would predict because:A) gravity is acting. B) one can never throw the ball fast enough. C) ideally the ball would never land. D) air friction slows the ball. E) all of the above.
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14. A ball is thrown straight upward at 20 m/s. Ideally (no air resistance), the ball will return to the thrower’s hand with a speed of:A) 0 m/s B) 40 m/s. C) 20 m/s. D) 10 m/s. E) There is not enough information to say.
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14. A ball is thrown straight upward at 20 m/s. Ideally (no air resistance), the ball will return to the thrower’s hand with a speed of:A) 0 m/s B) 40 m/s. C) 20 m/s. D) 10 m/s. E) There is not enough information to say.
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1. The brakes of an automobile can decelerate it at 6.00 m/s2. A) How many seconds are needed to stop the automobile if it is traveling at the rate of 54.0 m/s? B) How many meters does the automobile travel during this deceleration?
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(A)
v = v0 + at0 = 54 + (-6)tt = 9 s
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(B)
x = v0 t + ½ at2
x = 54(9) + ½ (-6)(9)2
x = 243 m
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(B) OR
v2 = v02 + 2ax
02 = 542 + 2(-6)xx = 243 m
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2. The surface gravity of the moon is 0.16 that of the earth. If a person’s mass is 140 kg, what is the person’s weight on the moon?
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140 x 10 x 0.16 =
224 N
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3. A cat starts from rest and accelerates for 5 seconds at 3 m/s2. Then it continues for 2 seconds at a constant speed. Construct a velocity vs. time graph AND a displacement vs. time graph to describe this motion.
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The velocity vs time graph will have a constant positive slope to 5 seconds then the line will become horizontal.The position vs time graph will have an upward parabolic curve to 5 seconds then a straight line with a positive slope.
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4. Briefly explain why a basketball being thrown toward the hoop is considered projectile motion.
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It is launched (horizontal velocity), only gravity acts on the ball, and air resistance is negligible.
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5. Briefly explain why the true path of a projectile traveling through Earth’s atmosphere is not a parabola.
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Air resistance affects the path.
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6. On point 0, a force of 25.0 N acts eastward and a force of 10.0 N acts southward. Calculate the magnitude and direction of the resultant force.
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252 + 102 = c2
c = 27 Ntan= 10/2522° south of east
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7. A plane flying level at 1000 m/s drops a bomb. The bomb hits its target on the ground 10 s later. How high was the plane flying? What is the horizontal distance the bomb travels while falling?
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y = v0 t + ½ gt2
y = 0( t) + ½ (10)102
y = 500 m
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1000 m/s x 10 s = 10000 m
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8. What vertical distance does a ball fall in 5.0 seconds when dropped from rest? What vertical distance does it fall if it has an initial horizontal velocity of 10 m/s?
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y = v0 t + ½ gt2
y = 0( t) + ½ (10)52
y = 125 m
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y = 125 mHorizontal velocity doesn’t affect the time of fall.
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9. A ball is thrown horizontally from the top of a tall cliff. Neglecting air drag, what vertical distance has the ball fallen 5.0 seconds later?
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y = v0 t + ½ gt2
y = 0( t) + ½ (10)52
y = 125 m
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