HW08-solutions

# HW08-solutions - dang(ttd73 – HW08 – Tsoi –(58020 1...

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Unformatted text preview: dang (ttd73) – HW08 – Tsoi – (58020) 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 (part 1 of 5) 10.0 points A child weighing 38 N climbs onto the right end of a see-saw, little knowing that it is tied down with a rope at its left end. The see-saw is 2 . 9 m long, weighs 11 N and is tilted at an angle of 22 ◦ from the horizontal. The center of mass of the see-saw is half way along its length, and lies right above the pivot. l θ What torque does the weight of the child exert about the pivot point? Take counter- clockwise to be positive. Correct answer:- 51 . 0878 N m. Explanation: τ C = M C g parenleftbigg l 2 parenrightbigg cos θ = 38 N 2 . 9 m 2 cos 22 ◦ =- 51 . 0878 N m . 002 (part 2 of 5) 10.0 points What torque does the weight of the see-saw exert about the pivot point? Take counter- clockwise to be positive. Correct answer: 0 N m. Explanation: This must be zero since the center of mass of the see-saw is just at the center, namely at the pivot. 003 (part 3 of 5) 10.0 points What torque does the rope exert about the pivot point? Take counter-clockwise to be positive. Correct answer: 51 . 0878 N m. Explanation: Since the see-saw doesn’t rotate, the total torque should be zero. The torque which balances the torque of the child is from the rope. They have opposite directions but the same magnitude. 004 (part 4 of 5) 10.0 points What force does the rope exert downwards on the see-saw? Give a positive answer....
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HW08-solutions - dang(ttd73 – HW08 – Tsoi –(58020 1...

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