Machine Kinematics

Laws of Solid Friction and Limiting Friction

Question 1
Marks : +2 | -2
Pass Ratio : 100%
The magnitude of the limiting friction (F ) bears a constant ratio to the normal reaction (RN) between the two surfaces.
True
False
Explanation:
The magnitude of the limiting friction (F ) bears a constant ratio to the normal reaction (RRN) between the two surfaces. Mathematically
Question 2
Marks : +2 | -2
Pass Ratio : 100%
A body of mass 400 g slides on a rough horizontal surface. If the frictional force is 3.0 N, find the magnitude of the contact force.
5 N
10 N
15 N
20 N
Explanation:
Let the contact force on the block by the surface be F which makes an angle Ï´ with the vertical.
Question 3
Marks : +2 | -2
Pass Ratio : 100%
The force of friction always acts in a direction, ___________ to that in which the body tends to move.
same
opposite
both of the mentioned
none of the mentioned
Explanation:
The force of friction always acts in a direction, opposite to that in which the body tends to move.
Question 4
Marks : +2 | -2
Pass Ratio : 100%
The ratio of magnitude of the kinetic friction to the normal reaction between the two surfaces is_____________ than that in case of limiting friction.
greater
less
equal
none of the mentioned
Explanation:
The magnitude of the kinetic friction bears a constant ratio to the normal reaction between the two surfaces. But this ratio is slightly less than that in case of limiting friction.
Question 5
Marks : +2 | -2
Pass Ratio : 100%
A heavy box of mass 20 kg is pulled on a horizontal surface by applying a horizontal force. If the coefficient of kinetic friction between the box and the horizontal surface is 0.25, find the force of friction exerted by the horizontal surface on the box.
29 N
39 N
49 N
59 N
Explanation:
As the box slides on the horizontal surface, the surface exerts kinetic friction on the box. The magnitude of the kinetic friction is
Question 6
Marks : +2 | -2
Pass Ratio : 100%
The force of friction is _____________ of the area of contact, between the two surfaces.
dependent
independent
both of the mentioned
none of the mentioned
Explanation:
The force of friction is independent of the area of contact, between the two surfaces.
Question 7
Marks : +2 | -2
Pass Ratio : 100%
A body of mass 400 g slides on a rough horizontal surface. If the frictional force is 3.0 N, find the angle made by the contact force on the body with the vertical.
350
360
370
380
Explanation:
Let the contact force on the block by the surface be F which makes an angle Ï´ with the vertical.
Question 8
Marks : +2 | -2
Pass Ratio : 100%
The force of friction does not depends upon the roughness of the surfaces.
True
False
Explanation:
The force of friction depends upon the roughness of the surfaces.
Question 9
Marks : +2 | -2
Pass Ratio : 100%
The magnitude of the force of friction is ____________ to the force, which tends the body to move.
equal
different
both of the mentioned
none of the mentioned
Explanation:
The magnitude of the force of friction is exactly equal to the force, which tends the body to move.
Question 10
Marks : +2 | -2
Pass Ratio : 100%
For moderate speeds, the force of friction
increases
decreases
remains constant
none of the mentioned
Explanation:
For moderate speeds, the force of friction remains constant. But it decreases slightly with the increase of speed.