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Chapter 2 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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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/s 2. 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. Acceleration is best defined as the CHANGE in: A) velocity of an object. B) distance divided by time interval. C) time it takes to move from one speed to another speed. D) time it takes to move from one place to another place. E) velocity divided by the time interval.

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5. In the absence of air resistance, objects fall at constant: A) speed. B) distances each successive second. C) velocity. D) acceleration. E) all of the above

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6. Suppose you take a trip that covers 240 km and takes 4 hours to make. Your average speed is: A) 60 km/h. B) 120 km/h. C) 240 km/h. D) 960 km/h. E) 480 km/h.

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7. A ball is thrown straight up. At the top of its path its instantaneous speed is: A) about 50 m/s. B) 0 m/s. C) about 5 m/s. D) about 10 m/s. E) about 20 m/s.

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1. The engine of an automobile can accelerate it at 6.00 m/s 2. A) How many seconds are needed to accelerate the automobile to a speed of 54.0 m/s? B) How many meters does the automobile travel during this acceleration?

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(A) v = v 0 + at 54 = 0 + 6t t = 9 s

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(B) x = v 0 t + ½ at 2 x = 0(9) + ½ 6(9) 2 x = 243 m

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(B) OR v 2 = v 0 2 + 2ax 54 2 = 0 2 + 2(6)x x = 243 m/s

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2. You toss a ball upward at 40.0 m/s. How much time will the ball take to reach the top of its path?

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v = v 0 + gt 0 = 40 + (-10)(t) t = 4 s

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3. A crate falls from an airplane flying horizontally at an altitude of 3,000 m. How long will it take the crate to reach the ground?

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y = v 0 t + ½ gt 2 3000 = 0( t) + ½ (10)t 2 t = 24.5 s

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4. A lemming runs off the edge of a cliff. After it has fallen 30 m, what is the lemming’s velocity?

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v 2 = v 0 2 + 2gy v 2 = 0 2 + 2(10)30 v 2 = 600 v = 24.5 m/s

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5. A stone is dropped from a cliff. After it has fallen 40 m, what is the stone’s velocity?

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v 2 = v 0 2 + 2gy v 2 = 0 2 + 2(10)40 v 2 = 800 v = 28.3 m/s

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