Question

A 20kg block is initially at rest. A 70N force is required to set the block in motion. After the motion, a force of 60N is applied to keep the block moving with constant speed. The coefficient of static friction is

• A. 0.6
• B. 0.52
• C. 0.44
• D. 0.35

Answer 1

The correct option is D 0.35

To set a block in motion from rest require more force than to keep it into motion.
So, $70$ N is static condition(To start from rest) force and $60$ N is kinetic condition force.
Static friction co-efficient $=$ $\mu$
Normal force on block(N) $=$ m$\times$g $=$ 20 $\times$10 $=$ 200 N
Static friction force = $\mu$ N $=$ $70$
$\mu$ $\times$ 200 $=$ $70$
$\mu$ $=$0.35