eve roof PHYSICS 2110 FALL 2015 TEST 3 Instructor Dr. Alex Holloway 1.) A 4-kg p
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eve roof PHYSICS 2110 FALL 2015 TEST 3 Instructor Dr. Alex Holloway 1.) A 4-kg plank 200 cm long is supported at the 110 cm mark. A 6-kg mass hangs from it at the 150-cm mark. What is the position at which one would hang a 10 kg mass to keep the system in equilibrium? normal force at the fulcrum? cm mark. What is the 2.) A wheel was initially revolving at 260 rev/min. When a motor driying the wheel was switched off, it rotated through 19.5 revolutions before coming to rest. (a) Find out the constant angular acceleration of the wheel. (b) How long does it take the wheel to stop?Explanation / Answer
net Weight mg will always acts on the board at its centre so it is 1m
since net torque = 0
Torque of ct =
applying the moment balance about the fulcrum
T net = 0
distance of 6 Kg from fulcrum=150 - 110 = 40 cm
distance of center of ruler from fulcrum= 100 - 110 = -10 cm
assuming distance of 10 kg from fulcrum = x
so now
m1 r1- m2r2 + m2 x = 0
6*40 -4*10 +10*x=0
x = -20 cm
thus the position of 10 kg =110-20 = 20 cm mark
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B. net Normal Force = summ of mg
F = (10+4+6)* 9.8
F = 196 N
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2. initial angular velocity Wo = 260 rev/min = 260 * 2pi/60 = 27.22 rad/s
angular dispalcement theta = 19.5 rev = 19.5* 2pi = 1225.22 radians
use the equation Wf^2 -Wo^2 = 2 A S
where A is angular acceration
A = 27.22^2/(2 * 1225.22)
A = 0.302 rad/s^2
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use Wf = Wo + At
so t = Wf/A
t = Wf/A = 27.22/0.302
t = 90 secs
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