Question

Suppose we have block of 4 kilogram kept on a horizontal surface and we are applying a horizontal force of 10 newton. Let the coefficient of friction is 0.2. Find the force of friction. Assume that $g=10.$}

• A. 4 newton
• B. 8 newton
• C. 1 newton
• D. None of the above

Hint:

Friction cannot exceed $\mu mg$ on a horizontal surface.

Answer 1

The Correct Option is B

Step 1: Concept
Limiting friction $f_L = \mu N$.
Step 2: Analysis
Normal force $N = mg = 4 \times 10 = 40$ N. $\mu = 0.2$.
Step 3: Calculation
Maximum friction force $f_L = 0.2 \times 40 = 8$ N. Applied force = 10 N. Since the applied force (10 N) is greater than the limiting friction (8 N), the block will move, and the frictional force acting is the kinetic friction (assumed equal to 8 N here).
Step 4: Conclusion
The force of friction is 8 newton.
Final Answer:(B)