A block weighing 15N rests on a flat surface and a horizontal force of 3N is exerted on it. Determine the frictional force on the block

Physics Jamb, Waec, Neco Past Questions & Answers on FRICTIONAL FORCE

QUESTIONS 5: A block weighing 15N rests on a flat surface and a horizontal force of 3N is exerted on it. Determine the frictional force on the block.

Ans:3N WAEC 2001

Solution:

Weight (W) = R = Force of gravity =15N

Horizontal force = Applied force (F) = 3N

Since the block is not accelerating, the motion is static.

So using, F(s)= U(s)×F(n)

Where F(s) = Force of static friction

μ(s) = Coefficient of static friction

F(n) = Normal force

Recall that, U(s) = Applied force (F)/Force of gravity (W) = F/W 

μ = F/R

μ = 3/15 = 0.2

Also, On a flat surface, the Normal force (Fn) = Force of gravity = Weight (W)

Therefore, Fs = μ ×Fn

Fs = 0.2×15 = 3N