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QUESTION: 1

Gravitational force does not depend on:

Solution:

The Gravitational force between two bodies does not depend on the charge of two bodies.

It is F = Gm1m2 / R^{2}

QUESTION: 2

The value of ‘g’ is minimum:

Solution:

The value of 'g' that is gravity is greater at the poles because the gravitational pull is maximum at the poles and decreases as it comes down toward the equator.

QUESTION: 3

Weight of an object is highest at

Solution:
By the universal law of Gravitation Force is directly proportional to the product of their masses and Force is inversely proportional to the square of their distances. .Then, we also know that weight is also a form of force.A the distance of the pole is least from the center of the earth.So, the force of attraction is highest on the body at poles . Hence ,the weight of a body is highest.

QUESTION: 4

Apple falls towards the earth but the earth does not move towards the apple because

Solution:

Apple falls towards the earth, but the earth does not move towards the apple because acceleration is inversely proportional to mass. Earth’s mass being extremely large as compared to apple, it has negligible acceleration towards the apple.

QUESTION: 5

What is the mass of a body whose weight is 59 N? Take g = 9.8 m/s^{2}

Solution:
Force = 59 N......... g = 9.8 m/s²......Since, F= m*g...which also gives m = F/g....m = 59/9.8 = 6.02 kg = 6 kg (approx.)

QUESTION: 6

A ball is thrown vertically upwards with a velocity ‘u’. The velocity with which it falls to the earth again is:

Solution:

For vertically upward motion: g is negative as it opposes the motion.

v = u – gt

0 = u – gt

t = u/g (1)

For vertically downward motion: g is positive as it is in the direction of motion.

v = u + gt

v = 0 + gt

t = v/g (2)

From equation 1 and 2

v = u

QUESTION: 7

Weight of a body on earth is 48 N; its weight on moon is

Solution:
G on moon is 1/6 of that of earth.So weight becomes 48/6=8

QUESTION: 8

Universal law of gravitation does not explain

Solution:

The motion of electrons in an atom is governed by electrostatic force, therefore the Universal law of gravity doesn't explain it.

QUESTION: 9

The mass of a body on earth is 60 kg, its mass on moon is

Solution:

A **mass** of **60kg** on **Earth** will exert a downwards force (**its** '**weight**') of **60** x 9.8 = 588N. A **mass** of **60kg** on the **Moon** will still be **60Kg** as **mass** is independent of gravity, but will 'weigh' about **60** x 1.3 = 78N. The **Moon's** gravity (**its** gravitational constant) is about 1/6th that of the **Earth's**.

QUESTION: 10

The value of acceleration due to gravity at the poles

Solution:
In combination, the equatorial bulge and the effects of the surface centrifugal force due to rotation mean that sea-level effective gravity increases from about 9.780 m/s2 at the Equator to about 9.832 m/s2 at the poles, so an object will weigh about 0.5% more at the poles than at the Equator.

QUESTION: 11

The force of gravitation between two bodies varies with r as:

Solution:

Gravitational force = Gm₁m₂ / r²

Where m₁ and m₂ are the masses of the two bodies,

We observe that m₁ , m₂ & G (gravitational constant) are constant

⇒ Gravitational force is inversely proportional to square of the distance between two bodies,

i.e, G ά 1/r²

QUESTION: 12

The magnitude of gravitational force between the earth and 10 kg body is:

Solution:
Gravity of earth is 9.8 N acceleration due to gravity is also 9.8 N gravitational force is nothing but the force applied by earth Therefore, f = m*a f,= 10*9.8 f= 98 N

QUESTION: 13

If the mass of earth is increased by 25% without any change in its size. Then, its acceleration due to gravity:

Solution:

The acceleration due to gravity on earth is given by g = GM/R^{2}

From the above equation, we observe that acceleration is directly proportional to the mass of the earth. So, **if the mass of the earth is increased by 25 % and R is kept constant, the value of g will also increase by 25%.**

QUESTION: 14

Which of following is not related to gravitational law?

Solution:
Motion of planets around the earth, rainfall and snowfall and occurrence of tides happen due to the gravitational force, whereas thunder lightning is an electrostatic phenomenon.

QUESTION: 15

How much gravitational force acts between two people of mass 60 kg each sitting at distance of 1 m apart?

Solution:
F= G m1m2/r^2.
F= 6.67× 10^-11 × 60 × 60/1^2.
F= 6.67 × 3600 × 10^-11/1.
F= 24012 × 10^-11.
F= 2.4 × 10^-7.

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