# UT PHY 317K - HW02-solutions (7 pages)

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## HW02-solutions

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- Pages:
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- School:
- University of Texas at Austin
- Course:
- Phy 317k - General Physics I

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gilbert hlg574 HW02 tsoi 55730 This print out should have 18 questions Multiple choice questions may continue on the next column or page find all choices before answering 001 part 1 of 2 10 0 points An elevator accelerates upward at 1 2 m s2 The acceleration of gravity is 9 8 m s2 What is the upward force exerted by the floor of the elevator on a n 65 kg passenger Correct answer 715 N Explanation 1 590 N 1 73 0N 601 N a What is the angle 1 which the righthand cable makes with respect to the ceiling Round up to four significant digits Express unit as degrees Correct answer 38 4808 degrees a Explanation Observe the free body diagram below N mg When the elevator is accelerating upward Fnet m a N m g N m a m g 002 part 2 of 2 10 0 points If the same elevator accelerates downwards with an acceleration of 1 2 m s2 what is the upward force exerted by the elevator floor on the passenger Correct answer 559 N Explanation a N mg When the elevator is accelerating downward Fnet m a m g N2 N2 m g m a 003 part 1 of 2 10 0 points Consider the 601 N weight held by two cables shown below The left hand cable had tension 590 N and makes an angle of with the wall The right hand cable had tension 730 N and makes an angle of 1 with the ceiling 2 F2 1 F1 Wg Note The sum of the x and y components of F1 F2 and Wg are equal to zero Given Wg 601 N F1 730 N 1 38 4808 2 90 Basic Concepts X Fx 0 F1x F1 cos 1 F12 cos2 1 X and Fy and F2x F2 cos 2 F22 cos2 2 1 2 0 F1y F2y F3y 0 F1 sin 1 F2 sin 2 F3 0 F1 sin 1 F2 sin 2 F3 F12 sin2 1 F22 sin2 2 2 F2 F3 sin 2 F32 since 3 F3 sin 3 F3 sin 270 F3 and F3 cos 3 F3 cos 270 0 gilbert hlg574 HW02 tsoi 55730 2 Solution Since sin2 cos2 1 and adding Eqs 2 and 3 we have F22 F12 2 F1 F3 sin 1 F32 F 2 F32 F22 sin 1 1 2 F1 F3 2 F3 F12 F22 1 arcsin 2 F1 F3 601 N 2 730 N 2 arcsin 2 730 N 601 N 590 N 2 2 730 N 601 N 38 4808 Why doesn t the rope break when he is supported as shown at the left above To answer this find the tension in the rope Correct answer 355 N 004 part 2 of 2 10 0 points b What is the angle which the left hand cable makes with respect to the wall Round up to four significant digits Express unit as degrees Correct answer 75 2391 degrees

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