Page 69 - Physics - XI

VIVA VOCE

Q1. Why do we make two observations with roller moving up and down?
Ans. To eliminate the eff ect of friction between the roller and inclined plane.

Q2. What is the normal reaction on the inclined plane?
Ans. The normal reaction is mg cos θ. There is no movement in this direction.

Q3. What do you mean by an inclined plane?
Ans. An inclined plane is one of the simple machines which is used for raising heavy loads by applying
less eff orts.
Q4. Does inclined plane act as a machine?
Ans. Yes, it does because of the use of inclined plane we can raise a heavy load by applying less force.

Q5. What are the applications of an inclined plane?
Ans. (i) Ramp of houses (ii) Ladder

(iii) A plank put at the back of a truck or a railway wagon for loading and unloading heavy goods.
Q6. Give the relation between downward force and angle of inclination of the plane.
Ans. The relation is W = mg sin θ which is the component of the weight of the body down the inclined
plane.

Q7. Give an example where the force of friction is in the same direction as the direction of motion.
(NCERT)

Ans. Walking. This is because when you walk, you have to exert a backward force on the ground, and the
result is a forward force from the ground (friction), and this pushes you forward.
Q8. What is the relation between downward force and angle of inclination of the plane? (NCERT)
Ans. Downward force W is,
W = mg sinθ

Q9. How will you ensure that the roller moves upward/downward with constant velocity? (NCERT)
Ans. When the angle of inclination is increased, then the value of mg sin θ increases, and frictional force
also increases. So, the net tension in the thread required to balance is (mg sin θ – f) or else the roller
will accelerate downwards.

COMPETENCY-BASED QUESTIONS
COMPETENCY-BASED QUESTIONS

Multiple Choice Questions

Q1. The maximum value of static friction when the body is at the verge of starting motion is
known as
a. static friction b. limiting friction c. impending motion d. angle of repose

Q2. Limiting friction of a body depends on
a. area of contact of surfaces b. the volume of the smaller body on larger surface

c. nature of surfaces d. the periphery of the contact surfaces

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