Chapter 3 Dynamic
Q.1 Define and explain
force?
Ans. force:-an agent which moves or tends to move a stationary body stops
or tends to stop a moving body or tends to change the speed or direction of
moving body is known as force.
Force is a vector quantity and its unit is Newton. One Newton
is that force that moves a body of one kg with the acceleration of 1m/sec2.
Q.2 state and explain
or Newton 1st law of motion?
Ans. Newton’s 1st law:-this law states that in the
absence of any external force a body in rest will always remain in rest and a
body in motion will always continue its motion in a straight line with uniform
speed.
Explanation:-this law
has two parts which are explained below.
In the 1st part, it is stated
that in the absence of any external force a stationary body will always be at
rest, for example, a book is laying on the table so it will remain stationary and
will not change it's by itself unless someone moves it by applying a force.
In 2nd parts it is
stated that moving will always move along a straight line unless someone
stops it by applying a force but when a ball is kicked it comes to the state of
rest after covering some distance it is because the force friction of air and the earth acts upon the ball each moment which compels it to stop.
Q.3 state and explain
law of inertia?
Ans.1 inertia:-Newton’s 1st law of
motion is also known as inertia “inertia” is the property of a body which
opposes any change in its state of rest or motion.
Explanation:-inertia depends upon the mass of a
body in fact mass is the measure of inertia. Greater the mass of a body greater
will be inertia greater force will be required to stop it e.g the inertia of
hard cricket ball is greater than the inertia of soft ball and greater force
will require to stop hard ball.
Examples:-(1) when a jerk is given to the
branch of a tree all fruits falls down from it because when branch comes into
motion at on at that time the fruits in rest and tends remain in rest as a
result + they separated and fall down.
(2)when a carpet is beaten with a stick. The
carpet set into motion suddenly while the dust particles are at rest and tends
to remain at rest and tends to remain at rest as a result they fly off from
carpet.
(3) when bus suddenly stops the lower past of
passenger comes into rest while the upper past is still in motion and tends to
remain in motion as a result the passenger falls forward.
(4) when a person jumps from a moving vehicle, his
feet come in contact with ground and comes to state of rest while the upper
part is still in motion and tends to remain in motion, As a result person gets
hurt.
(5) A parcel laying on the seat of a car move with
same as that of the car whe breaks are suddenly applied the comes into rest but
parcel is still in motion and tends to remain in motion due to inertia as a
result the parcel falls into the floor.
Q.4 state and explain Newton’s
2nd law in detail?
Ans. statement:-this law states that when a
force acts on a body on acceleration is produced in direction of force which is
directly proportional to the applied force but inversely proportional to the
mass of the body.
Explanation:- if we apply a force “f” on a body
of mass “m” and it produces acceleration “a” in the direction of applied force,
the it mathematical from is given as
a
Comparingeq (i) and eq(ii) we get,
a
=>a = (k)f/m ………….(iii)
If f = 1 N mass = 1kg
then k = 1 so by putting
k
= 1 we get a = f/m =>f/,m => = ma ……(iv)
Equation
(iv) represents the mathematical form of 2ndeq: of motion.
If we apply equal force on two bodies of different masses,
the acceleration of lighter body will be greater than the acceleration of heavy
body. Similarly greater the applied force greater will be the acceleration
produced.
Example :-when a cricketer catches the ball he
moves his hands backward. By doing so the acceleration of ball decreases and
the force of ball caching in hand is also decreases and by catching the ball
the cricketer feel less fain.
Q.5 state and explain Newton’s 3rd law with the the help of examples?
Ans. Newton s third law:- states that for every action there
is a reaction which is equal in its magnitude but opposite in direction.