An iron block of sides 5 cm x 8 cm x 15 cm has to be pushed along the floor.The force required will be minimum when the surface in contact with ground is
8 cm x 15 cm surface
8 cm x 5 cm surface
5 cm x 15 cm surface
force is the same for all surfaces
When two surfaces are coated with lubricant,then they
stick to each other
slide upon each other
roll upon each other
none of these
Assertion (A): Frictional forces are conservative forces.Reason(R): Potential energy can be associated with frictional forces.
Both A and R are true and R is the correct explanation of A
Both A and R are true but R is not correct explanation of A
A is true,but R is false
Both A and R are false
Friction is the result of
gravitational acceleration
molecular interaction
magnetic interaction
nuclear interaction
A horizontal force of 10 N is necessary to just hold a block stationary against a wall. The coefficient of friction between the block and the wall is 0.2. The weight of the block is
20 N
50 N
100 N
2 N
A block of mass 0.1 kg is held against a wall applying a horizontal force of 5 N on the block. If the co-efficient of friction between the block and the wall is 0.5, the magnitude of the frictional force acting on the block is
2.5 N
0.98 N
4.9 N
0.49 N
A drum of radius R and mass M ,rolls down without slipping along an inclined plane of angle θ.The frictional force
converts translational energy to rotational energy
dissipates energy as heat
decreases the rotational motion
decreases the rotational and translational motion
The upper half of an inclined plane of inclination θ is perfectly smooth while the lower is rough.A body starting from rest at the top comes back to rest at the bottom,if the coeffecient of friction for the lower half is given by
μ = sin θ
μ = cotθ
μ = 2 cosθ
μ = 2 tanθ
A block of mass 50 kg is placed on a rough inclined plane.The inclination is gradually increased to 30° when the block starts sliding down.Find the magnitude of the limiting friction.
375 N
245 N
275 N
200 N
If the normal force is doubled,then coefficient of friction is
halved
tripled
doubled
not changed