# QUIZ8Solutions

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Published on 31 Jan 2019
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QUIZ%7,%PHY%191%B,%Red,%Friday,%Oct%21,%2016%(20%pts)%%
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Question 1: Dr. Evil has tied a skier of mass 40 kg to a spring of force constant k = 8440 N/m at the top of a
frictionless incline as shown below. The spring is compressed initially by 1 m and her height above the
ground while tied (position A in figure) is 10 m. The skier manages to untie herself and simultaneously
release the spring so that she hurtles down the incline. At point B she jumps on to the back of her
stationary friend (mass = 60 kg). Together they glide off to safety over the frictionless flat surface with
a velocity vB.
a) 5 m/s b) 6 m/s c) 7 m/s d) 8 m/s
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a) What is her speed just before her collision with her friend? (7pts)
Other answers: Blue 17.5 m/s Green: 21.3 m/s
b) What is the value of vB? (3 pts)
Other answers: Blue 7 m/s Green 8.5 m/s
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## Document Summary

Evil has tied a skier of mass 40 kg to a spring of force constant k = 8440 n/m at the top of a frictionless incline as shown below. At point b she jumps on to the back of her stationary friend (mass = 60 kg). Together they glide off to safety over the frictionless flat surface with a velocity v. Other answers: blue 17. 5 m/s green: 21. 3 m/s: what is the value of v. Other answers: blue 7 m/s green 8. 5 m/s. Turn%sheet%over: 5. 5 m, 4. 5 m, 2. 7 m, 3. 6 m, 1. 8 m. Question 2: two masses, of mass 2m and m, are hung on strings of the same length. Use c. o. m. e. to find velocity of 2m just before collision. The ball 2m descends by h, so its loss in pe (2m)gh must equal its gain in ke (2m)vbefore. 2 (we get this by a straightforward consideration of. W nc is zero). (2m)gh = (2m)vbefore.