Gravitation Test

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Gravitation Test - 45

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Weekly Quiz Competition

Question 1
1 / -0

The SI unit of weight is.

A
kg wt

B
N

C
g wt

D
all the above

Solution

The weight of a body is , as the force with which the earth attracts it towards the centre.
$$W= \dfrac{GMm}{R^2 }= mg$$
$$g$$ (acceleration due to gravity) $$= \dfrac{GM}{R^2}$$
where,
$$G$$ is constant of gravitation, $$R$$ is distance from the centre if the earth, $$M$$ is the mass of the earth.
If the mass of the body $$‘m'$$ , the force of attraction of the earth or the $$‘W'$$ of the body is
$$W= mg$$
Weight is the force of attraction, its S.I. unit is same as that of S.I. unit of force .
The S.I. unit of weight is Newton (N).
Question 2
1 / -0

If a force of $$10\ N$$ acts on surfaces of areas in the ratio $$1 : 2$$, then the ratio of thrusts is:

A
$$1 : 2$$

B
$$2 : 1$$

C
$$3 : 1$$

D
$$1 : 1$$

Solution

The net force acting in a particular direction is known as thrust.
Thrust does not depend on the area. The effect of thrust depends on the area.
Therefore, the ratio of thrusts is $$1:1$$
Question 3
1 / -0

A body is lying on the surface of the earth. Suppose that the earth suddenly loses its power of attraction, then:

A
the weight of body will become zero

B
the weight of body will become infinity

C
the mass of the body will become zero

D
the body will vanish in air

Solution

$$\text{Weight of a body(W)}=m\times g$$
If the gravitation of the earth is lost then $$g=0$$
So, $$W=0$$
Question 4
1 / -0

The apparent weight of a body, weighing M kg-wt, during free fall is

A
Less than Mkg wt

B
More than M kg w

C
Equal to Mkg wt

D
Zero

Solution

During the free fall, the body will experience acceleration due to gravity in the downward direction and a pseudo acceleration in the upward direction which will also be equal to the acceleration due to gravity
$$\Rightarrow g_{net} =g+(-g) =0$$

$$\Rightarrow W_{apparent}=m\times g_{net} =0$$

Hence the correct answer is option $$D$$
Question 5
1 / -0

When an object falls freely to the earth, the gravitational force acting on the body

A
act opposite to the direction of motion

B
acts along the direction of motion

C
is a constant

D
is equal to zero

Solution

direction of acceleration is same as the force acting on the body.
as we know gravitational force is attracting always and direction of force is always towards the center of another body. and g is acceleration due to gravitational force, so direction of force/acceleration will be towards the center of earth.
Also force depends on distance between the two bodies so it is not constant.
so option B is correct.
Question 6
1 / -0

If a force of 10 N acts on two surfaces of areas in the ratio 1 : 2, then the thrust on them has the ratio

A
1:2

B
2:1

C
3:1

D
1:1

Solution

The force acting on an object perpendicular to the surface is called thrust.
And the thrust does not depend on the surface area. So the thrust on both the surface is of $$10 \ N$$.
$$\implies$$ Their ratio is $$1:1$$.
Question 7
1 / -0

A body is thrown vertically upwards and rises to a height of 10 m. The time taken by the body to reach the highest point is :

A
1.43 s

B
4.1 s

C
1.24 s

D
2.86 s

Solution

Using 1st equation of motion,
$$v=u+at$$
Final velocity of the body is zero, i.e. $$v = 0$$
Acceleration $$a = -g = -9.8 \ m/s^2$$
So, $$0=u-gt$$
$$\Rightarrow u=gt . . . (i)$$

Now let us consider 2nd equation of motion,
$$s=ut+\dfrac{1}{2}at^2$$
Height reached $$=10 \ m$$
Using (i), we get
$$\Rightarrow 10= (gt)t-\dfrac{1}{2}gt^2$$
$$\Rightarrow 10= \dfrac{1}{2}gt^2$$
$$\Rightarrow t = \sqrt{\dfrac{10 \times 2}{g}}$$
$$\Rightarrow t = \sqrt{\dfrac{10 \times 2}{9.8}}$$
$$\Rightarrow t = \sqrt{2.0408}$$
$$\Rightarrow t = 1.428 \approx 1.43 sec$$
Question 8
1 / -0

The force ofgravitation between two bodies of mass 1kg each separated by a distance of 1 m in vacuum is:

A
$$6.67 \times 10^{-9}N$$

B
$$6.67 \times 10^{-10}N$$

C
$$6.67 \times 10^{-11}N$$

D
$$6.67 \times 10^{-12}N$$

Solution

$$F = \displaystyle \frac{Gm_1 m_2}{r^2}$$
$$= \displaystyle \frac{6.67 \times 10^{-11} \times 1 \times 1}{(1)^2}$$
$$= 6.67 \times 10^{-11} N$$
Question 9
1 / -0

The weight of a body would not be zero :

A
at the centre of the earth

B
during a free fall

C
in interplanetary space

D
at the surface of the earth

Solution

Weight of a body is the gravitational force exerted on the body. At the surface of the earth the value of gravitational force is 9.8 N. Thus on the surface of the earth a body weighing 1 kg has a weight equal to 9.8 N independent of its state of motion. Hence a body at surface of the earth cannot be zero since the value of g at earth surface is 9.8 $$\dfrac{m}{s^2}$$.
Question 10
1 / -0

If a rock is brought from the surface of the moon

A
its mass will change

B
its weight will change, but not mass

C
both mass and weight will change

D
its mass and weight will remain the same

Solution

Weight of the body is the peoduct of mass and acceleration due to gravity and thus depends on the value of acceleration due to gravity.
However, mass of a body is independent of tge acceleration due to gravity.
So weight of the stone will change but the mass will remain unchanged.

Hence correct answer is option $$B$$

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Gravitation Test - 45

Result

Gravitation Test - 45

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SHARING IS CARING

Question 1

kg wt

N

g wt

all the above

Solution

Question 2

$$1 : 2$$

$$2 : 1$$

$$3 : 1$$

$$1 : 1$$

Solution

Question 3

the weight of body will become zero

the weight of body will become infinity

the mass of the body will become zero

the body will vanish in air

Solution

Question 4

Less than Mkg wt

More than M kg w

Equal to Mkg wt

Zero

Solution

Question 5

act opposite to the direction of motion

acts along the direction of motion

is a constant

is equal to zero

Solution

Question 6

1:2

2:1

3:1

1:1

Solution

Question 7

1.43 s

4.1 s

1.24 s

2.86 s

Solution

Question 8

$$6.67 \times 10^{-9}N$$

$$6.67 \times 10^{-10}N$$

$$6.67 \times 10^{-11}N$$

$$6.67 \times 10^{-12}N$$

Solution

Question 9

at the centre of the earth

during a free fall

in interplanetary space

at the surface of the earth

Solution

Question 10

its mass will change

its weight will change, but not mass

both mass and weight will change

its mass and weight will remain the same

Solution

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