Gravitation - NEET Physics Questions
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Gravitation

Question 41: moderate

For a planet having mass equal to mass of the earth but radius is one fourth of radius of the earth, Then escape velocity for this planet will be:

(2000)

1. $11.2\text{ km/s}$
2. $22.4\text{ km/s}$
3. $5.6\text{ km/s}$
4. $44.8\text{ km/s}$
View Answer

Escape velocity is given by $v_e = \sqrt{\frac{2GM}{R}}$. Since mass is constant and radius becomes one-fourth, $v_e$ increases by a factor of $\sqrt{4} = 2$. Thus, $v_p = 2 \times 11.2\text{ km/s} = 22.4\text{ km/s}$. Option B is correct.

Question 42: moderate

The escape velocity of a body on the surface of the earth is $11.2\text{ km/s}$. If the earth’s mass increases to twice its present value and radius of the earth becomes half, the escape velocity becomes:

(1997)

1. $22.4\text{ km/s}$
2. $44.8\text{ km/s}$
3. $5.6\text{ km/s}$
4. $11.2\text{ km/s}$
View Answer

Escape velocity is given by $v_e = \sqrt{\frac{2GM}{R}}$. When mass becomes $2M$ and radius becomes $R/2$, $v'_e = \sqrt{\frac{2G(2M)}{R/2}} = 2v_e$. Thus, $v'_e = 2 \times 11.2\text{ km/s} = 22.4\text{ km/s}$.

Question 43: easy

A ball is dropped from a spacecraft revolving around the earth at a height of $120\text{ km}$. What will happen to the ball?

(1996)

1. It will fell down to the earth gradually
2. It will go very far in the space
3. It will continue to move with the same speed along the original orbit of spacecraft
4. It will move with the same speed, tangentially to the spacecraft.
View Answer

When a ball is dropped from a spacecraft, it possesses the same orbital velocity as the spacecraft. Therefore, it continues to move with the same speed along the original orbit.

Question 44: easy

The escape velocity from earth is $11.2\text{ km/s}$. If a body is to be projected in a direction making an angle $45^{\circ}$ to the vertical, then the escape velocity is:

(1993)

1. $11.2 \times 2\text{ km/s}$
2. $11.2\text{ km/s}$
3. $\frac{11.2}{\sqrt{2}}\text{ km/s}$
4. $11.2\sqrt{2}\text{ km/s}$
View Answer

Escape velocity is a scalar quantity and is independent of the direction or angle of projection. It depends only on the mass and radius of the planet, remaining $11.2\text{ km/s}$.

Question 45: easy

The satellite of mass $m$ is orbiting around the earth in a circular orbit with a velocity $v$. What will be its total energy?

(1991)

1. $\left(\frac{3}{4}\right)mv^2$
2. $\left(\frac{1}{2}\right)mv^2$
3. $mv^2$
4. $-\left(\frac{1}{2}\right)mv^2$
View Answer

Kinetic energy of the satellite is $K = \frac{1}{2}mv^2$ and potential energy is $U = -mv^2$. Total energy $E = K + U = \frac{1}{2}mv^2 - mv^2 = -\frac{1}{2}mv^2$.

Question 46: easy

For a satellite escape velocity is $11\text{ km/s}$. If the satellite is launched at an angle of $60^{\circ}$ with the vertical, then escape velocity will be:

(1989)

1. $11\text{ km/s}$
2. $11\sqrt{3}\text{ km/s}$
3. $\frac{11}{\sqrt{3}}\text{ km/s}$
4. $33\text{ km/s}$
View Answer

The escape velocity formula depends solely on the gravitational potential and mass/radius of the body. It is independent of the angle at which the object is launched.

Question 47: easy

Two astronauts are floating in gravitational free space after having lost contact with their spaceship. The two will:

(2017-Delhi)

1. Move towards each other
2. Move away from each other
3. Will become stationary
4. Keep floating at the same distance between them
View Answer

Due to universal gravitational attraction between the two astronauts, they will experience a mutual attractive force and move towards each other in space.