Question

A 20 kg metal block is placed on a horizontal surface. The block just begins to slide when horizontal force of 100 N is applied to it. Calculate the coefficient of static friction. If coefficient of kinetic friction is 0.4 then find minimum force to maintain its uniform motion.

Answer 1

Answer:

Explanation:

Now force will be Static Friction. So F = μ s N, we can write N = mg where N is equal to weight of block, μs is coefficient of static friction.

F = 100 N

So F = μ s x mg

       100 =  μ s x 20 x 9.8

     So  μ s = 100 / 20 x 9.8

         μ  s =   0.5102

coefficient of static friction is 0.5102

According to Newton’s second law of motion Force = mass x acceleration

So Force – kinetic friction = mass x acceleration

Since acceleration is zero we get

Force – kinetic friction = 0

F – μk x mg = 0

F – 0.4 x 20 x 9.8 = 0

F – 78.4 = 0

F = 78.4 N

So minimum force to maintain its uniform motion is 78.4 N