2. A 20-kg block is pushed against a vertical wall by a horizontal force of 150

Question

2. A 20-kg block is pushed against a vertical wall by a horizontal force of 150 N as shown in the figure. The coefficient of static friction. s)between the block and the wall is 0.65: and the coefficient of kinetic friction, k, is 043) which one of the following statements is true, if the block is initially at rest? A) The total forcé exerted on the block by the wall is directed horizontally. B) The block will slide down the wall because the coefficient of kinetic friction is less than the coefficient of static friction. C) The block slides down the wall with an acceleration of magnitude 6.58 m/s D) The block will slide down the wall because the force of static friction can be no larger than 64.5 N B) The block will remain at rest because the coefficient of static friction is greater than the coefficient of kinetic friction. 150 y

Explanation / Answer

Given , normal reaction force on wall (N) = 150 N

s = 0.65 , k = 0.43, mass(m) = 20 kg

Static frictional force (fs)= s* N = 0.65*150 = 97.5 N

Kinetic frictional force (fk)= k*N = 0.43*150 = 64.5 N

Weight acting downward of the block(W) = 20*9.8 = 196 N

If the block is about to slide down , Kinetic frictional force acts on the block

Using Newton second law,

W - fk = m*a

196 - 64.5 = 20*a

a = 6.58 m/s^2

Therefore , answer) option C) the block slides down with an acceleration of 6.58 m/s^2

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