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Prelim_Exam__1_S05

# Prelim_Exam__1_S05 - Your Name Recitation Instructor's Name...

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Your Name 2 SHORT ANSWER [40 points] Please mark letters of your answers in spaces provided. 1. [4 points] Two boys, Abe and Bob, decide to race identical sleds down a frictionless hill. Abe + his sled have a mass of 50 kg, while Bob + his sled have a mass of 60 kg. (a) If both Abe and Bob start from rest at the same time at the top of the hill, who should reach the bottom of the hill first? (Ignore friction and air resistance.) (A) Abe (B) Bob (C) They both reach the bottom at the same time. Answer: Now the boys attach identical rocket engines to their sleds and race across level horizontal frictionless snow. If they start from rest at the same time and place, who wins the race? (Again, ignore friction and air resistance.) (A) Abe (B) Bob (C) They both reach the finish line at the same time. Answer: 2. [5 points] Three identical ideal springs, each having spring constant k, are connected as shown. What is the effective spring constant of this combination of springs? (A) k/3 (D) k (G) 2k Answer: (B) k/2 (E) 4k/3 (H) 3k (C) 2k/3 (F) 3k/2 3. [5 points] Shown is a portion of the graph of the vertical velocity v y (t) vs. time t for a beach ball of weight w that was tossed vertically into the air. The slope of the graph at points #1-3 has the values: slope #1 = - 0.7 g slope #2 = - 0.6 g slope #3 = - 0.5 g (a) What is the magnitude of the
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Prelim_Exam__1_S05 - Your Name Recitation Instructor's Name...

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