Homework Help: physics

Posted by kim on Monday, October 8, 2012 at 1:07pm.

A mass m1 = 10 kg on top of a rough horizontal table surface is connected by a massless cable over a frictionless wheel to a hanging mass m2 = 5 kg, as shown in the previous problem. In m2 falls 1 m from rest in 1.2 seconds, find the co-efficient of kinetic friction between m1 and the table surface.

also,

A mass m1 = 10kg resting on a rough horizontal table surface is connected by a massless cable over a frictionless wheel to a hanging mass m2= 5 kg,. What is the minimum co-efficent of static friction which will allow the masses to remain at rest?

physics - Elena, Monday, October 8, 2012 at 3:11pm
1.
h=at²/2
a=2h/t²= 2•1/1.2²=1.4 m/s²
m2•a =m2•g –T = > T = m2•g-m2•a.
m1•a=T-F(fr) = T-μ•N= T-μ•m1•g = m2•g-m2•a- μ•m1•g.
μ=[m2•g – a(m1+m2)]/m1•g = [5•9.8 – 1.4•15]/10•9.8 = 0.27.

2.
0 = m2•g –T

0=T-F1(fr) = T- μ(s) •m1•g
m2•g = μ(s) •m1•g,
μ(s) = m2/m1=5/10 = 0.5

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