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Friction — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysicsFriction1 Mark
Question
In a situation the contact force by a rough horizontal surface on a body placed on it has constant magnitude. If the angle between this force and the vertical is decreased, the frictional force between the surface and the body will:
  1. Increase.
  2. Decrease.
  3. Remain the saint.
  4. May increase or decrease.
✓

Answer

  1. Decrease.

Explanation:

According to the first law of limiting friction,

$\text{f}=\mu\text{N}$

where f is the frictional force

N is the normal reaction force

$\mu$ is the coefficient of static friction

and

$\text{N = mg}-\text{F}\cos\theta$

where m is the mass of the body

F is the contact force acting on the body

If we decrease the angle between this contact force and the vertical, then $\text{F}\cos\theta$ increases and the normal reaction force (N) as well as the frictional force (f) decrease.

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