Frictional force

Q.

Friction that exists between two surfaces in contact, when there is no relative motion between them is called as?

Q.

Gravel is strewn on the slippery ground during the rainy season to __________ friction.

Q. A box of mass $20kg$ is moving with a velocity of $2m{s}^{-1}$ on a rough floor. The box moves $5m$ on the floor before coming to rest. What must be the frictional force acting on the box?

1. 4 N
2. 2 N
3. 20 N
4. 8 N

Q.

Name the three kinds of friction.

Q.

A physicist is investigating the effect that different conditions have on the force of friction. The material used is an ordinary brick, with a mass of 1.8 kg. It is pulled across the surface of a wooden table. Friction is measured by pulling the brick with a string attached to a spring scale, calibrated in newtons (N). When the brick is pulled at constant speed, the reading on the scale is equal to the force of friction between the brick and the table top.
Experiment 1: The brick is placed on the table in three different positions. First, it is allowed to rest on its broad face (area $=180c{m}^2$), then on its side (area $=130c{m}^2$), and finally on its end (area $=56c{m}^2$)
Table 1
$\begin{array}{cccc}Area\left(c{m}^2\right)& 180& 130& 56\\ Friction\left(N\right)& 7.1& 7.3& 7.2\end{array}$

Experiment 2: A wooden block of mass 0.6 kg is made to the same dimensions as the brick, and the experiment is repeated.
Table 2
$\begin{array}{cccc}Area\left(c{m}^2\right)& 180& 130& 56\\ Friction\left(N\right)& 1.2& 1.1& 1.2\end{array}$

Experiment 3: The time, the wooden block is loaded by adding 1.2 kg of extra mass on top of it, to give it the same weight as the brick.
Table 3
$\begin{array}{cccc}Area\left(c{m}^2\right)& 180& 130& 56\\ Friction\left(N\right)& 3.5& 3.6& 3.7\end{array}$
From Experiment 1, it would be reasonable to hypothesize that:

1. The surface are of contact does not affect the amount of friction x

2. Friction is large in a brick-to-wood contact

3. Heavy objects have more friction that light ones

4. The amount of friction depends on the way the weight of the object is distributed.

Q. If a body moving along a horizontal surface comes to rest after travelling some distance. The force which is responsible for stopping the motion of the body here is called:

1. Electrostatic force
2. Magnetic force
3. Frictional force
4. Gravitational force

Q.

A man of mass m pulls a block with mass M with a rope. The block moves towards the right direction as shown in the figure below:

The magnitude of friction is the same between the man and the ground and between the block and the ground. If T is the tension on the rope, f is the frictional force acting on the block, which of the following expression correctly depicts the force experienced by the block ?

1. $T-f=M\times a_B$

2. $T-f=\frac{M}{a_B}$

3. $T+f=M\times a_B$

4. $\frac{T}{f}=M\times a_B$

Q.

A stone of $1kg$ is thrown with a velocity of $20m{s}^{-1}$ on the frozen surface of a lake. The stone comes to rest after travelling a distance of $50m$. What is the force of friction between the stone and the ice?

1. $4N$

2. $3N$

3. There is no friction between stone and ice

4. $5N$

Q. A moving body can continue moving on a frictionless surface only when a force is acting on it.

1. False
2. True

Q.

When a fast moving vehicle is suddenly stopped by applying the brake, the force that causes deceleration is exerted by the brake.

1. True

2. False

Q.

Friction exerted by surfaces on each other when they are at rest is called:

1. Static friction

2. Kinetic friction

3. Sliding friction

4. None of the above

Q.

The force of friction acting on a car on different roads in the increasing order of magnitude will be

1. Tar, concrete, gravel and mud roads

2. Concrete, tar, gravel and mud roads

3. Gravel, mud, tar and concrete roads

4. Mud, tar, concrete and gravel roads

Q. State true or false:
According to Galileo, friction is a force that stops objects in motion.

1. True
2. False

Q.

When a football player kicks a ball, he experiences a force on his leg which is equal to the force he exerted on the ball.

1. False

2. True