Friction Test

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Friction Test - 4

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Weekly Quiz Competition

Question 1
1 / -0

A box of mass M is lying on the flat bed of a pickup truck as shown. The truck is moving with a uniform velocity of 15 m/s. What is the value of force of friction between the mass and the bed of the truck?

A
15M N

B
7.5M N

C
5M N

D
0 N

Solution

As there is no relative motion between the surface of the box and the bed of the pickup truck, the force of friction acting on the box is zero.
Question 2
1 / -0

A porter pushes a box lying on a platform towards the East. In which direction does the force of friction act on the box?

A
North

B
East

C
West

D
South

Solution

The force of friction on the box acts towards the West as friction always acts in a direction opposite to the direction of relative motion between two surfaces.
Question 3
1 / -0

A flat bed truck is accelerating eastwards with an acceleration of 5 m/s². There is a box of mass M sitting loose on the bed of the pickup truck without slipping. What is the value of force of friction on the mass M?

A
0 N

B
1M N

C
2.5M N

D
5M N

Solution

As the base is moving without slipping, the acceleration of the box = acceleration of the truck
Hence, external force being exerted on the box = mass ^_x acceleration = M 5 N = 5M N
This external force is being provided by the force of friction between the bed of the truck and the surface of the box. Hence, value of force of friction on the box = value of external force on the box = 5M N
Question 4
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Which of the following statements is true?

A
Force of friction is the same for all surfaces.

B
Smoothing of a surface does not affect the distance traveled by a freely moving body over it.

C
Friction is caused by the irregularities on the two surfaces in contact.

D
The number of irregularities on a rough surface and a smooth surface are the same.

Solution

Friction is caused by the irregularities on the two surfaces in contact.
Question 5
1 / -0

A body of mass M just begins to move under the continuous application of a force F on a horizontal surface. If the force is continuously being applied, then what can you say about the speed with which the body is moving?

A
It does not change.

B
It continuously increases.

C
It continuously decreases.

D
Nothing can be said

Solution

Just as the body starts to move, the force of friction on the body changes from static friction to sliding friction. Now, the value of static friction on the body is F. Hence, the value of sliding friction on the body is less than F.
Let the value of sliding friction be f.
Now, net force on the body is F - f = f'.
Thus, the body is under the action of net external force of value f'. Hence, it will accelerate.
Question 6
1 / -0

There are 4 cubes A, B, C and D of identical materials. Their masses are m, 2 m, 4 m and 8 m, respectively. Which of the four is easiest to push on a surface?

A
A

B
B

C
C

D
D

Solution

As A is the lightest, it is the easiest to push as force of friction on it is the lowest. This is because its weight is the lowest and it presses onto the surface with the least amount of force.
Question 7
1 / -0

Which of the following statements is true?

A
The force of friction between two surfaces decreases as they are pressed harder.

B
The force of friction between two surfaces increases as they are pressed harder.

C
Static friction is smaller than sliding friction.

D
Static friction is equal to sliding friction.

Solution

When we press the two surfaces harder, the force of friction between the two surfaces increases.
Question 8
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The force required to overcome friction at the instant an object starts moving from rest is a measure of _______ and the force required to keep the object moving with the same speed is a measure of ________.

A
sliding friction, static friction

B
static friction, rolling friction

C
static friction, sliding frictions

D
rolling friction, static friction

Solution

The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction and the force required to keep the object moving with the same speed is a measure of sliding friction.
Question 9
1 / -0

Which of the following statements is false?

A
The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction.

B
The force required to keep the object moving with the same speed is a measure of sliding friction.

C
The force required to keep the object moving with an increasing speed is a measure of sliding friction.

D
The force required to keep an object moving with the same speed under effect of friction is lesser than the force required to move it from rest under the effect of friction.

Solution

Static friction is the friction which comes into play when the object tries to the move but actually it is not moving , under the action of the applied force.
When the object is moving with constant speed on the rough horizontal force it means that resultant force acting on it is zero hence we can say the frictional force acting on the body is equal and opposite to the applied force.
When the object is moving with increasing speed on the rough horizontal force it means that resultant force acting on it is non- zero hence we can say the applied force acting on the body is more than the frictional force hence the statement the force required to keep the object moving with an increasing speed is a measure of sliding friction is false.
Kinetic friction is always less than the limiting friction which the maximum static friction hence we can say the force required to keep an object moving with the same speed under effect of friction is lesser than the force required to move it from rest under the effect of friction.
Question 10
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Which of the following is not an advantage of friction?

A
A nail is fixed in the wall due to friction.

B
When a class teacher is writing with chalk on the blackboard, its rough surface rubs off some chalk particles due to friction which stick to the blackboard.

C
Automobile tires wear out with time due to friction.

D
Striking a matchstick produces light due to friction.

Solution

Automobile tires wear out with time due to friction.
Question 11
1 / -0

Which of the following statements is/are incorrect?

A
Friction can never be entirely eliminated.

B
Friction can be reduced by wing lubricants.

C
A perfectly smooth surface with no irregularities can be fabricated.

D
All of the above

Solution

The surfaces of bodies are never perfectly smooth. Even a very smooth surface seen under a microscope is found to have depressions and projections.
Question 12
1 / -0

Which of the following statements is true?

A
Application of lubricant reduces the area of contact between the two bodies, thus reducing friction.

B
Applyication of lubricant such as oil reduces the force by which the surfaces are pressed against each other due to buoyancy, thus reducing friction.

C
Application of lubricant forms a thin film of lubricant on the two surfaces preventing direct contact, thus reducing friction.

D
All of the above

Solution

When lubricant is applied between the two surfaces , a thin layer is formed there and moving surfaces do not directly rub against each
other and interlocking of irregularities is avoided to a great extent. Movement becomes smooth.
Question 13
1 / -0

Sliding in most machines is replaced by rolling by the use of

A
axles

B
gears

C
ball bearings

D
hubs

Solution

Sliding in most machines is replaced by rolling by the use of ball bearings. Ball bearing provide rolling friction which is less than sliding friction.
Question 14
1 / -0

The technical name for the friction force exerted by fluids on objects in motion through them is called

A
sliding friction

B
static friction

C
drag

D
resistance

Solution

The frictional force exerted by fluids is also called drag.
Question 15
1 / -0

On which of the following factors does the drag experienced by a body moving through air depends?

(a) Mass of the body
(b) Shape of the body
(c) Speed of the body

A
Both (a) and (b)

B
Both (a) and (c)

C
Both (b) and (c)

D
All of the above

Solution

Drag does not depend on the mass. It just depends on the shape of the body and the speed. Two bodies of the same mass can experience different values of drag.

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Re-Attempt Weekly Quiz Competition

Friction Test - 4

Result

Friction Test - 4

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Rank

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SHARING IS CARING

Question 1

15M N

7.5M N

5M N

0 N

Solution

Question 2

North

East

West

South

Solution

Question 3

0 N

1M N

2.5M N

5M N

Solution

Question 4

Force of friction is the same for all surfaces.

Smoothing of a surface does not affect the distance traveled by a freely moving body over it.

Friction is caused by the irregularities on the two surfaces in contact.

The number of irregularities on a rough surface and a smooth surface are the same.

Solution

Question 5

It does not change.

It continuously increases.

It continuously decreases.

Nothing can be said

Solution

Question 6

A

B

C

D

Solution

Question 7

The force of friction between two surfaces decreases as they are pressed harder.

The force of friction between two surfaces increases as they are pressed harder.

Static friction is smaller than sliding friction.

Static friction is equal to sliding friction.

Solution

Question 8

sliding friction, static friction

static friction, rolling friction

static friction, sliding frictions

rolling friction, static friction

Solution

Question 9

The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction.

The force required to keep the object moving with the same speed is a measure of sliding friction.

The force required to keep the object moving with an increasing speed is a measure of sliding friction.

The force required to keep an object moving with the same speed under effect of friction is lesser than the force required to move it from rest under the effect of friction.

Solution

Question 10

A nail is fixed in the wall due to friction.

When a class teacher is writing with chalk on the blackboard, its rough surface rubs off some chalk particles due to friction which stick to the blackboard.

Automobile tires wear out with time due to friction.

Striking a matchstick produces light due to friction.

Solution

Question 11

Friction can never be entirely eliminated.

Friction can be reduced by wing lubricants.

A perfectly smooth surface with no irregularities can be fabricated.

All of the above

Solution

Question 12

Application of lubricant reduces the area of contact between the two bodies, thus reducing friction.

Applyication of lubricant such as oil reduces the force by which the surfaces are pressed against each other due to buoyancy, thus reducing friction.

Application of lubricant forms a thin film of lubricant on the two surfaces preventing direct contact, thus reducing friction.

All of the above

Solution