A. Medical labs often use centrifuges to separate the different components of bl
ID: 1785677 • Letter: A
Question
A. Medical labs often use centrifuges to separate the different components of blood or tissue. In a centrifuge, materials are whirled rapidly so they experience a large centripetal force. What is the force acting on a 0.276 g blood sample rotating at 170 revolutions per minute at a radius of 0.1 m?
B. A car rounds a flat circular track with radius 336 m. The coefficient of static friction between the tires and track is 0.223. What is the maximum speed for the car if it's to stay on the track? Give your answer in m/s.
C. A wooden block slides down a 20 degree incline with acceleration 1.67 m/s2. Find the coefficient of kinetic friction.
D. A 1.68-kg book is at rest on a wooden board inclined at 15 degrees. Find the magnitude of the force of static friction.
E. A piece of steel rests on a wooden board, with frictional coefficient of 0.388 between the steel and the board. Find the maximum inclination angle for the board before the steel begins sliding.
Explanation / Answer
(A) w = 170 x 2pi rad / 60s = 17.8 rad/s
F = m w^2 r = (0.276 x 10^-3) (17.8^2) (0.1)
F = 8.75 x 10^-3 N
(B) f = m v^2 / r
u m g = m v^2 /r
v= sqrt(0.223 x 9.81 x 336) = 27.1 m/s
(C) a = g (sin20 - uk cos20)
sin20 - uk cos20 = 1.67/9.81
uk = 0.18
(D) F = m g sin15 = 4.27 N
(E) u = tan(theta)
theta = tan^-1(0.388) = 21.2 deg