–/3 points OSColPhys1 5.P.012.Tutorial.WA.My Notes Alex is asked to move two box
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Question
–/3 pointsOSColPhys1 5.P.012.Tutorial.WA.My Notes
Alex is asked to move two boxes of books in contact with each other and resting on a rough floor. He decides to move them at the same time by pushing on box A with a horizontal pushing force FP = 8.9 N. Here A has a mass mA = 10.2 kg and B has a mass mB = 7.0 kg. The contact force between the two boxes is
The coefficient of kinetic friction between the boxes and the floor is 0.02. (Assume
acts in the +x direction.)
(a) What is the magnitude of the acceleration of the two boxes?
m/s2
(b) What is the force exerted on mB by mA? In other words what is the magnitude of the contact force
N
(c) If Alex were to push from the other side on the 7.0-kg box, what would the new magnitude of
be?
N
Explanation / Answer
FP = 8.9 N
mA = 10.2 kg
mB = 7.0 kg
u = 0.02
(a)
Let the acceleration of the two boxes be a.
Net Mass, M = mA + mB
M = 10.2 + 7.0 = 17.2 Kg
Force = Mass * Acceleration
Fp - Fs = M*a
Where Fs is the Friction Force, = u* Mg
8.9 - u* Mg = M*a
8.9 - 0.02*17.2*9.8 = 17.2 * a
a = 0.32 m/s^2
Acceleration of the two boxes, a = 0.32 m/s^2
(b)
Force exerted on mB by mA ,
Fc - Fs = mB*a
Fc = mB*a + Fs
Fc = 7.0 * 0.32 + 0.02*7.0*9.8 N
Fc = 3.612 N
(c)
New value would be,
Fc = mA * a + Fs
Fc = 10.2 * 0.32 + + 0.02*10.2*9.8 N
Fc = 5.26 N
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