The ultracentrifuge is an important tool for separating and analyzing proteins i
ID: 1481686 • Letter: T
Question
The ultracentrifuge is an important tool for separating and analyzing proteins in biological research. Because of the enormous centripetal accelerations that can be achieved, the apparatus must be carefully balanced so that each sample is matched by another on the opposite side of the rotor shaft. Failure to do so is a costly mistake. Any difference in mass of the opposing samples will cause a net force in the horizontal plane on the shaft of the rotor. Suppose that a scientist makes a slight error in sample preparation, and one sample has a mass 9.0 mg greater than the opposing sample.
If the samples are 10 cm from the axis if the rotor and the ultracentrifuge spins
at 7.3×104 rpm , what is the magnitude of the net force on the rotor due to the unbalanced samples?
Express your answer using two significant figures.
__________N
Explanation / Answer
centripetal accleration is
ac = v^2/r
v = d/t
= 7.3 * 10 ^4 ( 2 pi (0.10 m)/ 60 s
=764.06 m/s
ac = ( 764.06 m/s)^2/0.10 m = 5837978.71 m/s^2
from the newton second law
F = ma = (9 * 10 ^-6 kg( 5837978.71 m/s^2 ) = 52.54 N
for two siginiifant figures 53 N
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