laws of motion

Question 1

what is forces and its types

Answer 1

A push or a pull exerted on any object, is defined to be a force. It is a vector quantity.
Force can be grouped into two types:
contact forces , non-contact forces

Question 2

what are contact forces

Answer 2

Contact forces are the forces that act between two bodies in contact, e.g. tension,
normal reaction, friction etc.

Question 3

what are non-contact forces

Answer 3

Non-contact forces are the forces that act between two bodies separated by a distance
without any actual contact. e.g. gravational force between two bodies and electrostatic
form between two charges etc.

Question 4

what is inertia

Answer 4

The inability of a body to change by itself its state of rest or state of uniform motion along
a straight line is called inertia of the body.

Question 5

first law of motion(law of inertia)

Answer 5

It states that a body continues to be in a state of rest or of uniform motion along a straight
line, unless it is acted upon by some external force the change the state. This is also
called law of inertia.
● This law defines force.
● The body opposes any external change in its state of rest or of uniform motion.
● It is also known as the law of inertia given by Galileo.

Question 6

linear momentum

Answer 6

p=mv

Its unit is kg-ms–1 and dimensional formula is [ML T –1]

Question 7

second law of motion

Answer 7

The rate of change of momentum of a body is directly
proportional to the applied force and takes place in the
direction in which the force acts
F=Kdp/dt where k is constant
f=ma
The SI unit of force is newton ( ) N and in CGS system is dyne.
1 105 N = dyne

Question 8

impulse

Answer 8

I=F(average)T
also impulse is equal to change to momentum
I=p2-p1

Question 9

Third Law of Motion

Answer 9

To every action, there is an equal and opposite reaction.

F12= -F21

Question 10

principle of conservation of momentum

Answer 10

It states that if no external force is acting on a system, the
momentum of the system remains constant.
F=dp/dt
if no force is acting then F=0
m1v1=m2v2

Question 11

friction

Answer 11

a force opposing the relative
motion starts acting between these two surfaces in contact. It
is known as friction or the force due to friction

Question 12

static friction

Answer 12

n It is the opposing force that comes into
play when one body is at rest and a force acts to move it
over the surface of another body.
It is a self adjusting force and is always equal and opposite
to the applied force.

Question 13

limiting friction

Answer 13

It is the limiting (maximum) value of
static friction when a body is just on the verge of starting
its motion over the surface of another body.
f=μN
where, µl
is the coefficient of limiting friction for the
given surfaces in contact.

Question 14

kinetic friction

Answer 14

It is the opposing force that comes into
play when one body is actually slides over the surface of
another body.

Question 15

rolling friction

Answer 15

f=μN/r

where are is radius of the object

Question 16

application of conservation of linear momentum

Answer 16

upwards thurst on the rocket, F= -udm/dt-mg and if effect of gravity is neglected then mg is not considered

Question 17

instantaneous upward velocity of rocket

Answer 17

v=u ln(Mo/m)-gt and neglecting the effect of gravity
v=2.303 u log10(Mo/m)
m0 = initial mass of the rocket including that of the
fuel,
u = initial velocity of the rocket at any time t,
m = mass of the rocket left,
v = velocity acquired by the rocket

Question 18

rate of combustion of fuel

Answer 18

dm/dt

Question 19

Burnt out speed of the rocket is the speed attained by the
rocket when the whole of fuel of the rocket has been burnt.
Burnt out speed of the rocket

Answer 19

vb=u log e(Mo/Mr)=3.303 u log10(Mo/Mr)

Question 20

apparent weight of a boy in a lift

Answer 20

If lift is accelerating upward with acceleration a, then
apparent weight of the body is R=(g+a)

If lift is accelerating downward at the rate of acceleration a, then apparent weight of the body is R=m(g-a)

If lift is moving upward or downward with constant
velocity, then apparent weight of the body is equal to
actual weight.

If the lift is falling freely under the effect of gravity, then itis called weightlessness condition.