Question

A block of mass \( 5 \, \text{kg} \) is placed on a horizontal surface. The coefficient of friction between the block and the surface is \( 0.4 \). What is the force of friction acting on the block?

• A. \( 20 \, \text{N} \)
• B. \( 15 \, \text{N} \)
• C. \( 10 \, \text{N} \)
• D. \( 25 \, \text{N} \)

Hint:

Remember: The force of friction depends on both the coefficient of friction and the normal force, which is equal to the weight of the object when on a horizontal surface.

Answer 1

The Correct Option is A

Calculate the Force of Friction

We are given the following data:

• Mass of the block \( m = 5 \, \text{kg} \)
• Coefficient of friction \( \mu = 0.4 \)
• Acceleration due to gravity \( g = 9.8 \, \text{m/s}^2 \)

Step 1: Calculate the normal force

The normal force is equal to the weight of the object: \[ N = m \cdot g = 5 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 49 \, \text{N} \]

Step 2: Calculate the force of friction

The force of friction is given by: \[ f_{\text{friction}} = \mu \cdot N = 0.4 \times 49 \, \text{N} = 19.6 \, \text{N} \] Rounding to the nearest whole number: \[ f_{\text{friction}} = 20 \, \text{N} \]

Conclusion:

The force of friction acting on the block is \( 20 \, \text{N} \).

The correct answer is:

Option 1: 20 N