HW #7-3-solutions

# HW #7-3-solutions - pasha(sep635 HW 7-3 Antoniewicz(56445...

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pasha (sep635) – HW 7-3 – Antoniewicz – (56445) 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A certain motor is capable of doing 1500 J of work in 17 s. What is the average power output of the motor? Correct answer: 88 . 2353 W. Explanation: P = W t = 1500 J 17 s = 88 . 2353 W . 002 (part 1 of 2) 10.0 points If you follow a diet of 2000 food calories per day (2000 kilocalories), what is your average power consumption in watts? (1 calorie=4.2 J.) Correct answer: 97 . 2 W. Explanation: P = (2000 cal)(1000)(4 . 2 J) (24 hr)(3600 s) = 97 . 2 W. 003 (part 2 of 2) 10.0 points You can produce much higher power for short periods of time. Suppose you run up a flight of stairs of height h = 6 m in Δ t = 15 s. Estimate your average power output if your total body mass is m = 65 kg. You can neglect friction or any other dissipative forces in your calculation. Use g = 9 . 8 m / s 2 . Correct answer: 254 . 8 W. Explanation: P = m g h Δ t = (65 kg)(9 . 8 m / s 2 )(6 m) 15 s = 254 . 8 W . 004 (part 1 of 3) 10.0 points Consider a horizontal spring-mass system with sti ff ness 204 N / m and mass 0 . 4 kg. The system is released with an initial compression of the spring of 0 . 11 m and an initial speed of the mass of 3 m / s. What is the maximum stretch of the spring during the motion, neglecting friction?

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