Solved: PHYSICS Question for NEET

NEET PHYSICSEasy

On the horizontal surface of a truck ( $\mu = 0.6$ ), a block of mass 1 kg is placed. If the truck is accelerating at the rate of $5 \text{ m/s}^2$ , then the frictional force on the block will be:

5 N

6 N

5.88 N

8 N

Step-by-Step Solution

Analyze Forces: The truck accelerates at $a = 5 \text{ m/s}^2$ . For the block of mass $m=1 \text{ kg}$ to move along with the truck (stay stationary relative to it), a force is required. In the frame of the truck, a pseudo force $F_p = ma$ acts on the block opposite to the acceleration. $F_{req} = ma = 1 \text{ kg} \times 5 \text{ m/s}^2 = 5 \text{ N}$
Calculate Limiting Friction: The maximum possible static friction ( $f_{max}$ ) is determined by the coefficient of friction $\mu$ and the normal reaction $N$ ( $N=mg$ ). $f_{max} = \mu mg = 0.6 \times 1 \text{ kg} \times 9.8 \text{ m/s}^2 = 5.88 \text{ N}$ (If $g=10 \text{ m/s}^2$ , $f_{max} = 6 \text{ N}$ ).
Conclusion: The required force ( $5 \text{ N}$ ) is less than the limiting friction ( $5.88 \text{ N}$ ). Therefore, the block does not slide. Since static friction is self-adjusting (it adjusts to match the applied force up to the limit), the frictional force acting on the block is exactly equal to the force required to accelerate it [Source 67, 68]. $f_s = F_{req} = 5 \text{ N}$

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