Friction General Understanding

Q.

Can the coefficient of friction be more than one?

Q. 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. $\text{increase}$
2. $\text{decrease}$
3. $\text{remain same}$
4. $\text{may increase or decrease}$

Q.

Coefficient of friction between $5kg$ and $10kg$ block is $0.5$. If friction between them is $20N$, the value of force being applied on $5kg$ (in $N$) is (Assume that the floor is frictionless)

Q.

A 40 kg slab rests on a frictionless floor. A 10 kg block rests on top of the slab. The static coefficient of friction between the block and the slab is 0.60 while the kinetic coefficient is 0.40. The 10 kg block is acted upon by a horizontal force of 100 N. If g = 9.8m/s², then what will be the resulting acceleration of the slab?

Q.

On the horizontal surface of a truck (µ=0.6), a block of mass 1 kg is placed. If the truck is accelerating at the rate of 5m/sec^{​​​​2} then frictional force on the block will be

Q. If ${\mu }_r,{\mu }_k$ and ${\mu }_s$ represent the coefficients of rolling friction, kinetic friction and static friction, then

1. ${\mu }_r>{\mu }_k>{\mu }_s$
2. ${\mu }_r<{\mu }_k>{\mu }_s$
3. ${\mu }_r<{\mu }_k<{\mu }_s$
4. ${\mu }_r>{\mu }_k<{\mu }_s$

Q. Two equally charged, identical metal spheres A and B repel each other with a force 'F'. The spheres are kept fixed with a distance 'r' between them. A third identical, but uncharged sphere C is brought in contact with A and then placed at the mid-point of the line joining A and B. The magnitude of the net electric force on C is

1. F
2. $\frac{F}{2}$
3. $\frac{3F}{4}$
4. $\frac{F}{4}$

Q.

• What is action at a distance force?

Q. Two cars of unequal masses use similar tyres. If they are moving at the same initial speed, the minimum stopping distance

1. $\text{is smaller for the heavier car}$
2. $\text{is smaller for the lighter car}$
3. $\text{depends on the volume of the car}$
4. $\text{is same for both cars}$

Q.

A sphere rolls without slipping on an inclined plane of inclination . Then the minimum value of coefficient of friction so that the sphere rolls with out slipping is

1. 

2. 

3. 

4. 

Q.

How does the radius of the pulley affect the tensions in the belt?

Q. A horse has to pull harder during the start of motion than later. Explain.

Q. A block of mass $5\text{kg}$ is resting on a rough horizontal surface. Now a force of $24N$ is imparted to it with a negligible impulse as shown in the figure. If the coefficient of kinetic friction is 0.4 and $g=10{\text{m/s}}^2$, then the acceleration of the block will be

1. $0.26m/s^2$
2. $0.39m/s^2$
3. $0.69m/s^2$
4. $0.8m/s^2$

Q.

A horse continues to apply a force in order to move a cart with a constant speed. Explain why?

Q. A block of mass $10\text{kg}$ rests on a horizontal table. When it is hit by a bullet of mass $50\text{g}$ moving with speed $V$, it gets embedded in the block. The block moves , and comes to rest after moving a distance of $2\text{m}$ on the table. If a freely falling object were to acquire speed $\frac{V}{10}$ after being dropped from a height $H$, then neglecting energy losses and taking $g=10\text{m}/{\text{s}}^2$ find the value of $H$.
[Take coefficiant of friction between the block and the table to be $0.05$]

1. $0.05\text{km}$
2. $0.02\text{km}$
3. $0.03\text{km}$
4. $0.04\text{km}$

Q.

A small block B is placed on another block A of mass 5 kg and length 20 cm. Initially the block B is near the right end of block A Figure. A constant horizontal force of 10 N is applied to the block A. All the surfaces are assumed frictionless. Find the time elapsed before the block B separates from A.

Q. Why rolling friction is less than sliding friction?

Q. A block is shot with an initial velocity of $5\text{m/s}$ on a rough horizontal plane. Find the distance covered by the block till it comes to rest. Given the coefficient of friction between the surfaces of contact is $0.2\text{and}g=10m/s^2$.

1. $12\text{m}$
2. $25\text{m}$
3. $6.25\text{m}$
4. $20\text{m}$

Q. A system of two blocks as shown in the figure is initially at rest. Find the frictional force $f$ between the blocks as they are pulled by the forces as shown in the figure.

1. f = 25 N
2. f = 10 N
3. f =12 N
4. f = 15 N

Q.

Which of the following material is likely to have the least friction?

1. Wood

2. Glass

3. Paper

4. Plastic

Q. A cubical block rests on a plane of $\mu =\sqrt{3}$. The angle through which the plane should be inclined to the horizontal so that the block just slides down will be

1. ${45}^{\circ }$
2. ${60}^{\circ }$
3. ${75}^{\circ }$
4. ${30}^{\circ }$

Q. Find the direction of friction on A and B at the surfaces of contact between them (for the figure shown).

1. $\text{Left, Right}$
2. $\text{Right, Right}$
3. $\text{Right, Left}$
4. $\text{Left, Left}$

Q. In the figure shown, find the direction of friction on blocks B and C at the surface which is common to the blocks B and C respectively.

1. $\text{Forward, Backward}$
2. $\text{Backward, Forward}$
3. $\text{Backward, Backward}$
4. $\text{Forward, Forward}$

Q. The retarding acceleration of $4m/s^2$ due to frictional force stops a block of mass $40kg$ moving on a rough horizontal surface. The coefficient of friction between the block and the surface is

1. $0.3$
2. $0.4$
3. $0.55$
4. $0.65$

Q. In the figure shown, the coefficient of friction between all surfaces in contact is $0.4$. Taking $g=10m/s^2$, find the tension $T$ in the string.

1. $10N$
2. $12N$
3. $14N$
4. $20N$

Q.

In the following figure, find the direction of friction on the blocks $A$ and $B$ and the ground respectively.

1. $\text{Backwards, forwards, backwards}$
2. $\text{Forwards, backwards, forwards}$
3. $\text{Backwards, backwards, forwards}$
4. $\text{Forwards, forwards, backwards}$

Q.

What is rolling friction? What is the need of converting sliding friction into rolling friction?

Q. A block is shot with an initial velocity of $5m/s$ on a rough horizontal plane. Find the distance covered by the block till it comes to rest. Given coefficient of friction between the surfaces of contact is $0.1\text{and}g=10m/s^2$.

1. $5m$
2. $10m$
3. $12.5m$
4. $25m$

Q. From a lift moving upward with a uniform acceleration $a$, a man throws a ball vertically upwards with a velocity $v$ relative to the lift. The ball comes back to the man after time $t$. Which relation is correct ?

1. $a+g=2v/t$
2. $a+g=v/t$
3. $a+g=3v/t$
4. $a+g=4v/t$

Q.

A 40 kg slab rests on a frictionless floor as shown in the figure. A 10 kg block rests on the top of the slab. The static coefficient of friction between the block and slab is 0.60 while the kinetic friction is 0.40. The 10 kg block is acted upon by a horizontal force of 100 N. If g = 9.8 m/s², the resulting acceleration of the slab will be.

1. 1 m/s²

2. 1.5 m/s²

3. 2 m/s²

4. 6 m/s²