Homework 5, energy 19-20-problems.pdf - smedley(tws933 – Homework 5 energy 19-20 – dowd –(WilsonRPHY11920 1 This print-out should have 27

# Homework 5, energy 19-20-problems.pdf - smedley(tws933 –...

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smedley (tws933) – Homework 5, energy 19-20 – dowd – (WilsonRPHY11920 1) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points This question is typical on some driver’s li- cense exams: A car moving at 48 km / h skids 15 m with locked brakes. How far will the car skid with locked brakes at 144 km / h? Assume that energy loss is due only to sliding friction. Answer in units of m. 002 10.0points Two identical objects are moving directly to- ward one another at the same speed v . vectorv - vectorv m m What is the total kinetic energy of the sys- tem of the two objects? 1. 4 m v 2 since (2 v ) 2 = 4 v 2 2. Zero since ( vectorv - vectorv ) 2 = 0 3. None of these 4. m v 2 since energy is a scalar 5. Still 1 2 m v 2 from the definition of kinetic energy 003 10.0points Shawn and his bike have a total mass of 51 . 7 kg. Shawn rides his bike 1 . 2 km in 12 . 4 min at a constant velocity. The acceleration of gravity is 9 . 8 m / s 2 . What is Shawn’s kinetic energy? Answer in units of J. 004(part1of3)10.0points The current theory of the structure of the Earth, called plate tectonics, tells us that the continents are in constant motion. Assume that the North American continent can be represented by a slab of rock 5300 km on a side and 37 km deep and that the rock has an average mass density of 2720 kg / m 3 . The continent is moving at the rate of about 4 . 8 cm / year. What is the mass of the continent? Answer in units of kg. 005(part2of3)10.0points What is the kinetic energy of the continent? Answer in units of J. 006(part3of3)10.0points A jogger (of mass 77 kg) has the same kinetic energy as that of the continent. What would his speed be? Answer in units of m / s. 007(part1of2)10.0points A force vector F = F x ˆ ı + F y ˆ acts on a particle that undergoes a displacement of vectors = s x ˆ ı + s y ˆ where F x = 8 N, F y = - 2 N, s x = 5 m, and s y = 2 m.

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