Question

A horizontal force of 6N is applied to a block of mass 4kg resting on a rough horizontal
table having u= 0.2. If the block does not move on the table, how much frictional force (in
N) the table is applying on the block.​

Answer 1

Given

• Force Applied = 6 N
• Mass = 4 kg
• μ = 0.2

To Find

• Frictional force of the table on the block

Solution

● Fₛ = μmg

✭ Frictional Force :

→ Fₛ = μmg

• Fₛ = Frictional Force = ?
• μ = static Friction = 0.2
• m = Mass = 4 kg
• g = Gravitational Acceleration = 10 m/s²

→ Fₛ = 0.2 × 4 × 10

→ Fₛ = 2 × 4

→ Fₛ = 8 N

• So here as the Frictional Force was greater than the force applied the block didn't move

∴ Frictional force of the table on the block is 8 N

Answer 2

We know,

Frictional force = $\mu m g$

Force provided = 6 N

Mass = 4 kg

$\mu$ = 0.2 (static friction)

$\therefore$ Frictional force = (0.2)(4 kg)(9.8 m/s²)

$\leadsto$ 4/5 × 9.8 kg m/s²

$\leadsto$ 7.84 N (Answer).

To bring the block from rest to motion, we have to provide a force of magnitude of more than 7.84 N.