A 2.20 kg steel block is at rest on a steel table. A horizontal string pulls on

Question

A 2.20 kg steel block is at rest on a steel table. A horizontal string pulls on the block. The coefficient of static friction of dry steel on steel is s=.800, the coefficient of kinetic friction of dry steel on steel is k,dry=.600, and the coefficient of kinetic friction of lubricated steel on steel is k,lube=.050.

What is the minimum string tension needed to move the block?

If the string tension is 20.0 N , what is the block's speed after moving 1.00 m ?

If the string tension is 20.0 N and the table is coated with oil, what is the block's speed after moving 1.00 m ?

Explanation / Answer

a)

T = s*N = s*mg

Tmin = 0.80*2.20*9.8 = 17.24 N

b)

in case of motion kinetic friction will act

and T - k*mg = ma

20 - 0.6*2.20*9.8 = 2.20a

=> a = 3.21 m/s^2

V^2 = U^2 + 2aS
=> V^2 = 0 + 2*3.21*1

=> V = 2.53 m/s

c)

in this case of motion kinetic friction will act with value 0.050

and T - k*mg = ma

20 - .050*2.20*9.8 = 2.20a

=> a = 8.6 m/s^2

V^2 = U^2 + 2aS
=> V^2 = 0 + 2*8.6*1

=> V = 4.14 m/s

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