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ExamIIRevAnsFa07

# ExamIIRevAnsFa07 - RIII-1 An elevator is going up at a...

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RIII- 1. An elevator is going up at a constant speed. Near the top floor, it starts to slow to a stop. During the period that it is slowing down, its acceleration is A) downward. B) upward. C) in some other direction. Answer: Downwards v v 1 v 2 RIII- 2. Consider the vectors V 1 and V 2 shown. What is the direction of V = V 2 V 1 V 1 + V = V 2 v 1 direction of v? D v 2 C A B Answer: B) down RIII- 3. Consider the vector A G y Which equation is correct? A) A x = +A cos θ A θ B) A x = –A cos θ C) A x = +A sin θ D) A x = –A sin θ x Answer: A x = –A sin θ RIII- 4. A projectile is fired at an initial speed of v o at an angle of θ above the horizontal. Which of the following expressions could possibly be the correct expression for the range of the projectile? (Hint) check the units).

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( ) ( ) 2 0 o 2 o 2 o A) x 2g v tan B) x 2g v sin(2 ) v g C) x sin 2 D) x sin 2 g v = θ = = θ = θ θ Answer: C) only this expression has the units of distance RIII- 5. A plane in horizontal flight moving at constant velocity drops a heavy package while approaching the border of a kingdom. Which crosses the border first? (As usual, assume that air resistance is negligible.) A) the plane B) the package C) both cross at the same instant v = constant border Answer: Both cross at the same instant. RIII- 6. A boy of mass M = 50 kg pushes on a baby carriage of mass M/5 = 10 kg. The force on the carriage from the boy has magnitude F onCarriage . The force on the boy from the carriage handle has magnitude F onBoy . How do the forces compare? A) F onCarriage = 5 F onBoy B) F onCarriage = 0.2 F onBoy C) F onCarriage = F onBoy Answer: By Newton's third law, the forces must be the same magnitude (and opposite in the direction). RIII- 7. A heavy–duty truck pulling a light trailer is accelerating forward. How does the force on the truck F onTruck from the trailer compare to the force on the trailer F onTrailer from the truck?