Physics 217 Sample Exam 3 1. A 2.0 kg block is projected by a spring along a fri
ID: 1351476 • Letter: P
Question
Physics 217 Sample Exam 3 1. A 2.0 kg block is projected by a spring along a frictionless track to the portion of track with friction at the higher level. The spring constant is k = 200 N/m, and the initial compression is x = 1.2 m. The height difference of the two ends of the track is deltay = 5.0 m and the coefficient of kinetic friction between the block and upper surface is Muk = 0.6. Assume Ug1 = 0 at the initial level. Find: a) the initial spring potential energy, Us1, stored in the spring before it is released, b) the initial total mechanical energy, E1, of the block-spring system, c) the kinetic energy, K, of the block when it leaves the spring, d) the gravitational potential energy, Ug2, when the block reaches the new height, e) the kinetic energy of the block, K2, at the new height, just before it begins sliding with friction, f) the amount of work done by friction to stop the block, and, g) the distance, Kz, the block slides along the upper surface before stopping. 2. The system shown is at rest when the lower string is cut. The pulley and string are massless and the pulley is frictionless. Find: n) the change in gravitational potential energy, deltaU g, of the system when theExplanation / Answer
a) initial spring PE = kx^2 /2 = 200 (1.2^2) /2 = 144 J
b) initially block was at rest so KE= 0
initial ME = 144 J
c) using energy conservation,
mv^2 /2 = 144
v = sqrt(2 x 144 /2) = 12 m/s
d) Gravt. PE = mgh = 2 x 9.81 x 5 = 98.1 J
3) using energy conservationm,
PE + KE = 144
98.1 + KE = 144
KE = 45.9 J
f) Work done by friction = change in KE
Wf = 0 -45.9
Wf = - 45.9 J
g) friction force =uN = umg = 0.6 x 2 x 9.81 = 11.77 N
work done by friction = -fd = -45.9
d = 45.9 / 11.77 =3.90 m