Question

A block of mass 1 Kg lies on a horizontal surface in a truck. The coefficient of a static friction between the block and the surface is 0.6. What is the force of friction on the block if the acceleration of the truck is $5m/{s^2}$ ?
(Take \[g = 10m/{s^2}\] )
A. 5 N
B. 6 N
C. 7 N
D. 8 N

Answer 1

Hint: Friction is a self adjusting force. When a force acts on it friction can vary from 0 to its maximum value. Therefore, when a force acts upon a body, friction tends to move in the opposite direction. And there will be no movement of the body until the force acting upon it exceeds the maximum friction. Use this concept to reach the answer.
Formula used- $F = ma,{F_f} = \mu w,w = mg$

Complete Step-by-Step solution:
Mass of the block = 1 kg
Acceleration of the truck $ = 5m/{s^2}$
So, pseudo force acting on the block:
$F = ma = 1 \times 5N = 5N$
Coefficient of static friction $\mu = 0.6$
As we know that the static frictional force is given by:
$
  {F_f} = \mu w \\
  {F_f} = \mu mg \\
 $
So, the maximum value of static friction is:
$
   = \mu mg \\
   = 0.6 \times 1 \times 10N \\
   = 6N \\
 $
Friction is a self adjusting force. When a force acts on it friction can vary from 0 to its maximum value. Therefore, when a force acts upon a body, friction tends to move in the opposite direction. And movement of the body will not be there until the force acting on it exceeds the maximum friction.
Here the force acting on the block is 5N which is less than maximum friction (6N). So the friction will be 5N.
Hence, the force of friction on the block is 5N.
So, the correct answer is option A.

Note- Friction is the force that resists motion when the surface of one object comes in contact with the surface of another. A machine's mechanical advantage is diminished by friction, or in other words, because of friction the ratio of output to input is decreased. One-quarter of an automobile 's energy is used to minimize friction. However, it's also friction in the tyres that helps the vehicle to remain on the road and friction in the clutch, which makes driving easier. Frictional force is one of the most important forces in the world.