Page 70 - Physics - XI

Q3. Identify the correct statement.
a. Static friction depends on the area of contact

b. Kinetic friction depends on the area of contact
c. Coeffi cient of kinetic friction does not depend on the surfaces in contact
d. Coeffi cient of kinetic friction is less than the coeffi cient of static friction

Q4. The coeffi cient of static friction between two surfaces depends upon
a. the normal reaction b. the shapes of the surfaces in contact

c. the area of contact d. none of these
Q5. If the applied force is doubled, then coeffi cient of friction is

a. not changed b. tripled c. halved d. doubled

Q6. Which type of friction is experienced by a car rolling on a road?
a. Static friction b. Kinetic friction c. Rolling friction d. Fluid friction

Q7. Which of the following surfaces has the greatest coeffi cient of friction?
a. Smooth glass b. Wet ice c. Oiled metal d. Rough concrete

Q8. Which of the following is an example of static friction?
a. Pushing a heavy box across the fl oor b. Sliding down a hill on a sled
c. Pulling a suitcase along a carpeted fl oor d. None of these

Q9. Which of the following is an example of rolling friction?

a. Sliding a book across a table b. Skidding a bicycle on a wet road
c. A car driving on a smooth highway d. A ball rolling down a hill

Q10. During the padding of a bicycle, the force of friction exerted by the ground on the two wheels
is such that it acts
a. in the backward direction on the front wheel and in the forward direction on the rear wheel

b. in the forward direction on the front wheel and in the backward direction on the rear wheel
c. in the backward direction on both the front and the rear wheels
d. in the forward direction both the front and the rear wheels

Answer key

1. (b), 2. (c), 3. (d), 4. (a), 5. (a), 6. (c), 7. (d), 8. (d), 9. (d), 10. (a)

Case Study-based Questions

Read the paragraph and answer the questions that follow. f(N)

In a laboratory experiment on friction, a block of weight 135 N 75
lying on a rough horizontal table is pulled by a horizontal wire. 50
The pull (P) gradually increases until the block begins to move and 25
continues to increase thereafter. The given fi gure shows a graph P(N)
of the friction force (f) on this block as a function of the pull (P). 0 25 50 75 100

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