Punjab Text bool board, Physics.
Solution manual
Chapter 3 (Dynamics)
3.1 Encircle the correct answer from the given choices:
i. Newton's first law of motion is valid only in the absence of:
(a) force (b) net force (c) friction (d) momentum
ii. Inertia depends upon
(a) force (b) net force (c) mass (d) velocity
iii. A boy jumps out of a moving bus. There is a danger for him to fall:
(a) towards the moving bus (b) away from the bus (c) in the direction of motion (d) opposite to the direction of motion
iv. A string is stretched by two equal and opposite forces 10 N each. The tension in the string is
(a) zero (b) 5 N (c) 10 N (d) 20 N
v. The mass of a body:
(a) decreases when accelerated (b) increases when accelerated
(c) decreases when moving with high velocity (d) none of the above
vi. Two bodies of masses m1 and m2 attached to the ends of an inextensible string passing over a frictionless pulling such that both move vertically. The acceleration of the bodies is:
(a)( m1 x m2 / m1 + m2) g (b) (m1 - m2 / m1 + m2) g
(c) ( m1 + m2 / m1 - m2) g (d) (2m1m2 / m1 + m2) g
vii. Which of the following is the unit of momentum?
(a) Nm (b) kgms -1 (c) Ns (d) Ns-1
viii. When horse pulls a cart, the action is on the:
(a) cart (b) Earth © horse (d) Earth and cart
ix. Which of the following material lowers friction when pushed between metal plates?
(a) water (b) fine marble powder (c) air (d) oil
Short Questions
.2 Define the following terms: (i) Inertia (ii) Momentum (iii) Force (iv) Force of friction (v) Centripetal force.
Inertia:
The proper of an object due to which it oppose the change in its state is called Inertia
(ii) Momentum:
The product of mass and velocity of a moving object. It is also defined as the quantity of motion in an object.
(iii) Force:
That agent which tends or tends to change the state of an object is called a force. OR
The push and pull applied on an object is called a force.
(iv) Force of friction
The resistance offered by a surface of an object when another object moves over it is called the force of friction. OR
The force which resists the motion of an object is called force of friction.
(v) Centripetal force:
The force acting on an object moving in a circular path which attracts the object towards the center is called centripetal force. OR
That force which is responsible for a circular motion is called centripetal force. It is always directed towards the center.
3.3 What is the difference between: (i) Mass and weight (ii) Action and reaction (iii) Sliding friction and rolling friction
(i) Mass and weight:
The total amount of matter in an object is called its mass. it is a scalar quantity while
The force with which Earth attracts an object towards itself is called weight. It is a vector quantity
(ii) Action and reaction
The force exerted on an object by our hands is called action and the force exerted by the same object on our hands is called reaction.
(iii) Sliding friction and rolling friction:
the frictional force between the two object sliding over each other is called sliding friction. For example, the friction between a book sliding over a table surface.
where
The frictional force between any two surfaces when one surface is rolling over another is called Rolling friction. For example, The friction between the Tyre of a moving car and Earth's surface.
FYI : Rolling friction is always smaller than the sliding friction
3.4 What is the law of Inertia?
Ans) First law of motion is also called the law of inertia. it states that, A body continues its state of rest or of uniform motion until and unless an external force acts upon it.
( solution will be continued in next blog)
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