Acceleration Due to Gravity and its variation - NEET Physics Questions
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Acceleration Due to Gravity and its variation

Question 1: moderate

The acceleration due to gravity on the planet A is 9 times the acceleration due to gravity on planet B. A man jumps to a height of 2m on the surface of A. What is the height of jump by the same person on the planet B ?

1. 18 m
2. 6 m
3. 2/3 m
4. 2/9 m
View Answer

From Equations of motion

The height of a jump is inversely proportional to the acceleration due to gravity. Let \( h_A \) be the height of the jump on planet A, and \( h_B \) be the height of the jump on planet B. Also, let \( g_A \) and \( g_B \) represent the acceleration due to gravity on planets A and B, respectively.

Given:
- \( g_A = 9g_B \)
- \( h_A = 2 \, \text{m} \)

The ratio of heights is:

\[
\frac{h_B}{h_A} = \frac{g_A}{g_B} = 9
\]

Thus, the height on planet B is:

\[
h_B = 9 \times h_A = 9 \times 2 = 18 \, \text{m}
\]

So, the height of the jump on planet B is \( 18 \, \text{m} \).

 

Question 2: moderate

The diameter of two planets are in the ratio 4:1 and their mean densities in the ratio 1:2 the acceleration due to gravity on the planets will be in ratio :

1. 1 : 2
2. 2 : 3
3. 2 : 1
4. 4 : 1
View Answer

\[ g=\frac{GM}{R^{2}}= \frac{G\times \rho\frac{4}{3}\pi R^{3}}{R^{2}}=\frac{4G\rho\pi R}{3} \]

\[ \frac{g_{1}}{g_{2}}= \frac{R_{1}.\rho_{1}}{R_{2}.\rho_{2}}= \frac{4\times 1}{1\times 2}= \frac{2}{1} \]

 

Question 3: easy

The depth at which the value of acceleration due to gravity becomes 1/n times the value at the surface is (R be the radius of the earth) :

1. R/n
2. R/n²
3. R(n-1)/n
4. Rn/n-1
View Answer

The depth at which the acceleration due to gravity becomes \( \frac{1}{n} \) times the surface value is:

\[
d = \left( 1 - \frac{1}{n} \right) R
\]

where \( R \) is the radius of the Earth.

Question 4: easy

The height at which the weight of a body becomes 1/16th, its weight on the surface of earth (radius R), is :

1. 3R
2. 4R
3. 5R
4. 15R
View Answer

The weight of a body at height \( h \) is given by:

\[
W_h = W_0 \left( \frac{R}{R + h} \right)^2.
\]

To find \( h \) when \( W_h = \frac{1}{16} W_0 \):

\[
\frac{1}{16} = \left( \frac{R}{R + h} \right)^2.
\]

Taking the square root:

\[
\frac{1}{4} = \frac{R}{R + h}.
\]

Cross-multiplying gives:

\[
R + h = 4R ; h = 3R.
\]

Thus, the height is \( 3R \).

Question 5: moderate

Imagine a new planet having the same density as that of earth but it is 3 times bigger than the earth in size. If the acceleration due to gravity on the surface of earth is g and that on the surface of the new planet is g’, then :

1. g' = 3g
2. g' = g/9
3. g' = 9g
4. g'=27 g
View Answer

The acceleration due to gravity \( g' \) on the new planet can be calculated using the formula:

\[
g' = \frac{GM}{R^2}.
\]

For the new planet:

- Its radius \( R' = 3R \) (3 times the radius of Earth).
- Its mass \( M' \) is given by \( M' = \text{density} \times \text{volume} = \rho \times \frac{4}{3} \pi (R')^3 = \rho \times \frac{4}{3} \pi (3R)^3 = 27 \times \rho \times \frac{4}{3} \pi R^3 = 27M \) (mass is 27 times that of Earth).

Substituting into the formula:

\[
g' = \frac{G(27M)}{(3R)^2} = \frac{27GM}{9R^2} = 3g.
\]

Thus, \( g' = 3g \).

Question 6: easy

The height at which the acceleration due to gravity decreases by 36% of its value on the surface of the earth is: (Assume radius of the earth is R) :

1. R/4
2. R/2
3. R/6
4. 4R
View Answer

The height \( h \) at which gravity decreases by 36% (to 64% of its surface value) is found using:

\[
g_h = \frac{gR^2}{(R + h)^2}.
\]

Setting \( g_h = 0.64g \):

\[
0.64 = \frac{R^2}{(R + h)^2}.
\]

Taking the square root:

\[
0.8 = \frac{R}{R + h}.
\]

Cross-multiplying gives:

\[
0.8(R + h) = R \implies 0.8h = 0.2R \implies h = 0.25R=R/4
\]

Thus, the height is R/4.

Question 7: easy

The height at which the weight of a body becomes 1/16th, its height from the surface of earth (radius R), is :

1. 3R
2. 4R
3. 5R
4. 15R
View Answer

To find the height \( h \) at which the weight of a body becomes \( \frac{1}{16} \) of its weight on the surface of the Earth, use the formula:

\[
W_h = W_0 \left( \frac{R}{R + h} \right)^2.
\]

Setting \( W_h = \frac{1}{16} W_0 \):

\[
\frac{1}{16} = \left( \frac{R}{R + h} \right)^2.
\]

Taking the square root:

\[
\frac{1}{4} = \frac{R}{R + h}.
\]

Cross-multiplying gives:

\[
R + h = 4R ; h = 4R - R = 3R.
\]

Thus, the height is \( 3R \).

Question 8: moderate

A spherical planet has a mass Mp and diameter Dp. A particle of mass m falling freely near the surface of this planet will experience an acceleration due to gravity, equal to :

1. GMp/Dp²
2. 4GMpm/Dp²
3. 4GMp/Dp²
4. GMpm/ Dp²
View Answer

The acceleration due to gravity \( g \) on the surface of a spherical planet can be calculated using the formula:

\[
g = \frac{GM_p}{R_p^2},
\]

where:
- \( G \) is the gravitational constant,
- \( M_p \) is the mass of the planet,
- \( R_p \) is the radius of the planet.

Given that the diameter \( D_p = 2R_p \), we can express the radius as \( R_p = \frac{D_p}{2} \).

Substituting this into the formula gives:

\[
g = \frac{GM_p}{\left(\frac{D_p}{2}\right)^2} = \frac{GM_p}{\frac{D_p^2}{4}} = \frac{4GM_p}{D_p^2}.
\]

Thus, the acceleration due to gravity experienced by the particle near the surface of the planet is:

\[
g = \frac{4GM_p}{D_p^2}.
\]

Question 9: moderate

The change in the value of g at a height h above the surface of the earth is the same as at a depth d below the earth when both d and h are much smaller than the radius of the earth, which one of the following is correct ?

1. d = h/2
2. d = 3h/2
3. d = 2h
4. d = h
View Answer

The change in the value of \( g \) at height \( h \) above the surface of the Earth and at depth \( d \) below the surface can be expressed using the following formulas:

1. **At height \( h \)**:
\[
g_h = g \left(1 - \frac{2h}{R}\right) \quad \text{(for small } h\text{)}
\]

The change in \( g \) is:
\[
\Delta g_h = g - g_h = g \frac{2h}{R} = \frac{2gh}{R}.
\]

2. **At depth \( d \)**:
\[
g_d = g \left(1 - \frac{d}{R}\right) \quad \text{(for small } d\text{)}
\]

The change in \( g \) is:
\[
\Delta g_d = g - g_d = g \frac{d}{R}.
\]

Setting the changes equal gives:

\[
\frac{2gh}{R} = \frac{g d}{R}.
\]

Cancelling \( g \) and \( R \) (assuming they are non-zero):

\[
2h = d.
\]

Thus, the relation between depth \( d \) and height \( h \) is:

\[
d = 2h.
\]

Question 10: easy

If the rotational motion of earth is suddenly stopped then which one is correct :

1. Value of g decreases on all places of earth
2. Value of g increases on all places of earth except pole
3. Value of g increases on all places of earth
4. Value of g decreases on all places of earth except equator
View Answer

If the Earth's rotational motion were suddenly stopped, the value of \( g \) would effectively increase everywhere except at the poles due to the following reasons:

1. Centrifugal Force: The Earth's rotation creates a centrifugal force that slightly counteracts the force of gravity. At the equator, this effect is the greatest, reducing the apparent weight and thus the effective value of \( g \). When rotation stops, this centrifugal force disappears.

2. At the Poles: At the poles, there is no centrifugal force due to rotation since they are the axis of rotation. Therefore, the value of \( g \) would remain unchanged at the poles.

Consequently, \( g \) would increase at all places on Earth except at the poles, where it would stay the same.