Please choose 4 of the following 5 questions to answer (all parts of a question
ID: 2029659 • Letter: P
Question
Please choose 4 of the following 5 questions to answer (all parts of a question together count as a single question. 15 pts each): 1) On a horizontal surface, a crate with mass 40.0 kg is placed against a spring that stores 260J of energy. The spring is released, and the crate slides 5.60 m (after leaving contact with the spring) before coming to rest (due to friction). Assume the mass slides without friction while in contact with the spring. 3pts- a) What is the work done by friction in bringing the crate to rest? 5 pts- b) What is the coefficient of kinetic friction between the crate and floor? 7pts- c) What is the speed of the crate when it is 2.50 m from the spring?Explanation / Answer
a] Total work done = change in KE = 0
work done by friction + work done by spring = 0
work done by friction = - 260 J
b] Work done by friction = - uMg*d
260 = u*40*9.8*5.6
u = 260/[40*9.8*5.6]
= 0.118
c] energy lost by fricion = 260*2.5/5.6 = 116 J
energy left = 260 - 116 = 144 J
v = sqrt(2KE/m) = sqrt(2*144/40)
= 2.68 m/s answer