Question

A man is running on the ground. It is known that the coefficient of friction between the man and the ground is $\mu$ . Then which of the following statements is correct

• A. Normal reaction between man and ground is equal to weight of man
• B. The direction of friction on man is in the direction of normal reaction on the man
• C. Direction of friction on man is opposite to the direction of motion of man
• D. Maximum acceleration of man can be $2\mu g$

Answer 1

Answer: (A)

When we walk, our feet are pushing ground backwards and therefore the friction opposes the pushing and acts in the opposite direction which happens to be the direction in which we are walking.
Hence we can say friction works in the direction of walking

Normal reaction $N=Mg$ ( as per free body diagram )
Maximum acceleration $a_{max}=\frac{f_{max}}{M}=\frac{\mu Mg}{M}=\mu g$