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Friction — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 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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