Question 1) Question Part Points Submissions Used Objects with masses m1 = 12.0

Question

Question 1)

Question Part Points Submissions Used Objects with masses m1 = 12.0 kg and m2 = 8.0 kg are connected by a light string that passes over a frictionless pulley as in the figure below. If, when the system starts from rest, m2 falls 1.00 m in 1.80 s, determine the coefficient of kinetic friction between m1 and the table. The coefficient of static friction between the m = 2.95-kg crate and the 35.0 degree incline of the figure below is 0.295. What minimum force must be applied to the crate perpendicular to the incline to prevent the crate from sliding down the incline?

Explanation / Answer

a) let coeff of kinetic friction be Uk

then force on the mass m1 due to kinetic friction = m1*g*Uk =120Uk

net force on the system of 2 BLOCKS = m2g - 120Uk

therefore accn a of the system = (m2g - 120Uk)/(m1+m2) = 80-120Uk/20 = 4 - 6Uk

we know accn of both masses will be same

accn of m2 is :

S=1/2*a*t^2

therefore a = 2/(1.8^2) = 0.617 m/s^2

0.617 = 4 - 6Uk

therefore Uk = 0.56

b) static friction force "f" = Us*N N is the normal reaction force

N = F

f = mgsin(theta) = 2.95 * 10 * sin(35) = 16.92 N

16.92 = Us * F

therefore F = 57.35 N

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