A boy can jump to a height \$h\$ from ground on earth . What should be the radius of a sphere of density \$\delta \$ such that on jumping on it, he escapes out of the gravitational field of the sphere?

While jumping he converts his initial \$kinetic\$ \$energy\$ to \$potential\$ \$energy\$\$\dfrac{mv^2}{2}=mgh\$\$v=\sqrt{2gh}\$Now this \$ velocity\$ has to be equal to \$escape\$ \$velocity\$ on the sphere\$Escape\$ \$velocity=\sqrt{\dfrac{2GM_s}{R}}=\sqrt{\dfrac{8 \pi G R_s^2 \delta}{3}}\$By comparing both the velocities we get \$Radius(R_s)=\sqrt{\dfrac{3gh}{4 \pi G \delta}}\$

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>>Class 11
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>> $Hard Questions$

Gravitation

Q: A planet in a distant solar system is \$10\$ times more massive than the earth and its radius is \$10\$ times smaller. Given that the escape velocity from the earth is \$11 km\$ \$\mathrm{s}^{-1}\$, the escape velocity from the surface ofthe planet would be

\$Escape\ velocity= \sqrt { \dfrac { 2Gm }{ r } } \\ \dfrac { { v }_{ new } }{ { v }_{ earth } } = \sqrt { \dfrac { { m }_{ new }{ r }_{ earth } }{ { m }_{ earth }{ r }_{ new } } } = \sqrt { \dfrac { 10 }{ \dfrac { 1 }{ 10 } } }= 10\\ { v }_{ new }= 110\ km{ s }^{ -1 }\$

Q: At what distance above the surface of earth, the gravitational force will be reduced by \$10\%\$, if the radius of earth is \$6370\$ Km.

Gravitational force on the earth surface, \$F_{G_s}= \dfrac{GMm}{R^{2}}\$ Gravitational force at a height 'h' above, \$F_{G_{h}}= \dfrac{GMm}{(R+h)^{2}}\$ G.T. \$F_{G_{h}}= \dfrac{90}{100}(F_{G_{S}})\$ \$\Rightarrow \dfrac{GMm}{(R+h)^{2}}=\dfrac{9}{10}(\dfrac{GMm}{R^{2}})\$ \$\Rightarrow R+h=\sqrt{\dfrac{10}{9}}(R)\$ \$\Rightarrow 6370+h= \dfrac{3.162}{3} (6370)\$ \$\Rightarrow h=\dfrac{0.162 \times 6370}{3}=344\$ km

Q: The value of \$g\$ at a height \$h\$ above the surface of the earth is the same as at a depth \$d\$ below the surface of the earth. When both \$d\$ and \$h\$ are much smaller than the radius of earth, then which one of the following is correct

The value of gravity at a height \$h\$ above earth's surface is given by\$g_h=g\left(1-\dfrac {2h}{R}\right)\$and at a depth \$d\$ is given by \$g_d=g\left(1-\dfrac {d}{R}\right)\$Since these two values are same, we can see that \$d=2h\$

Q: A particle of mass 1kg is placed at a distance of 4m from the centre and on the axis of a uniform ring of mass 5kg and radius 3m. The work done to increase the distance of the particle from 4m to \$\sqrt{3}m\$ is.

Potential of a ring, \$V=\dfrac{-GM}{y}\$where, \$y=\sqrt{x^2+r^2}\$So initial, energy is \$\dfrac{-5G\times 1}{5}\$Final energy is \$\dfrac{-5G\times 1}{6}\$So the difference \$=\$ Final \$-\$ Initial \$=\dfrac{G}{6}\$

Q: A particle of mass \$10 gm\$ is kept on the surface of a uniform sphere of mass \$100 kg\$ and radius \$10 cm\$. Find the work done against the gravitational force between them, to take the particle far away from the sphere. \$\left ( G= 6.67\times10^{-11}Nm^{2}/Kg^{2} \right )\$

At infinity, the gravitational potential energy of the system will be \$0\$.Initially, the particle is outside sphere and hence sphere will behave as point object at its centre,Therefore,\${ E }_{ 0 }=-\dfrac { GMm }{ R } =-\dfrac { (6.67\times { 10 }^{ -11 })\times(100)\times(0.01) }{ 0.1 } =-6.67\times{ 10 }^{ -10 }J\$We know that, \$W=\Delta U=U_{f}-U_{i} \implies W=-U_{i}\$Thus, work done is \$6.67\times { 10 }^{ -10 }J\$

Q: The work done in shifting a particle of mass \$m\$ from the centre of earth to the surface of the earth is

Given,The mass of the particle be \$m\$,Initilly it is on the centre of the earth, soThe work done in moving a particle from center of earth to its surface\$\ W=\int_0^{R}Fdr\$\$=\int_0^R(-\dfrac{G(\rho\dfrac{4}{3}\pi r^3)m}{r^2})dr\$\$=\int_0^R(-\dfrac{4G\rho \pi mr}{3})dr\$\$=\dfrac{GMm}{2R},\$we know that \$F=\dfrac{GMm}{R^2}=mg\$\$=\dfrac{1}{2}mgR\$(Since \$g=\dfrac{GM}{R^2}\$)So, The work done in shifting a particle of mass from the centre of the earth to the surface of the earth is \$=\dfrac{mgR}{2}.\$

Q: The work done by an external agent to shift a point mass from infinity to the centre of the earth is W. Then choose the correct relation.

\$W_{ext}=\Delta U=U_{f}-U_{i}=U_{f}-0=U_{f}\$\$ W_{ext}=\displaystyle \frac{-3GMm}{2R} \rightarrow W_{ext}<0\$

Q: If g is the acceleration due to gravity on the earth's surface, the gain in the potential energy of an object of mass m raised from the surface of the earth to a height equal to the radius R of the earth, is:

Acceleration due to gravity on earth's surface\$=g=\dfrac{GM}{R^2}\$.Gain in potential energy=\$\dfrac{GMm}{R}-\dfrac{GMm}{2R}=\dfrac{GMm}{2R}=\dfrac{1}{2}mgR\$

Q: A particle hanging from a massless spring stretches it by 2 cm at earths surface. How much will the same particle stretch the spring at a height of 2624 km from the surface of the earth? (Radius of earth \$=\$ 6400 km).

\$g= \dfrac{GM}{R^{2}}\$ and \$g_{h}=\displaystyle \dfrac{GM}{(R+h)^{2}}\$\$ \Rightarrow \dfrac{g_{h}}{g}=\left(\dfrac{R}{R+h}\right)^{2}=\left(\dfrac{6400}{6400+2624}\right)^{2}=\dfrac{1}{2}\$\$\Rightarrow g_{h}=\displaystyle \dfrac{g}{2}\$At the surface of earth, \$mg = kx\$At the height \$\mathrm{h}' \Rightarrow mg_{h}=kx^{'}\$\$\displaystyle \Rightarrow\dfrac{g_{h}}{g}=\frac{x^{'}}{x}\Rightarrow x^{'}=\left(\dfrac{g_{h}}{g}\right)x=\left(\frac{1}{2}\right)(2cm)=1cm\$

Physics
2758 Views

JEE Mains NEET Easy Qs Med Qs Hard Qs

A planet in a distant solar system is $10$ times more massive than the earth and its radius is $10$ times smaller. Given that the escape velocity from the earth is $11 k m$ $s^{- 1}$ , the escape velocity from the surface ofthe planet would be

110 k m s^{- 1}

0.11 k m s^{- 1}

1.1 k m s^{- 1}

11 k m s^{- 1}

Hard

JEE Mains

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At what distance above the surface of earth, the gravitational force will be reduced by $10 %$ , if the radius of earth is $6370$ Km.

750 K m

650 K m

450 K m

344 K m

Hard

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The value of $g$ at a height $h$ above the surface of the earth is the same as at a depth $d$ below the surface of the earth. When both $d$ and $h$ are much smaller than the radius of earth, then which one of the following is correct

d = \frac{h}{2}

d = \frac{3 h}{2}

d = 2 h

d = h

Hard

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A boy can jump to a height $h$ from ground on earth . What should be the radius of a sphere of density $δ$ such that on jumping on it, he escapes out of the gravitational field of the sphere?

\frac{4 π G δ}{3 g h}

\frac{4 π g h}{3 G δ}

\frac{3 g h}{4 π G δ}

\frac{3 G δ}{4 π g h}

Hard

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A particle of mass 1kg is placed at a distance of 4m from the centre and on the axis of a uniform ring of mass 5kg and radius 3m. The work done to increase the distance of the particle from 4m to $3 m$ is.

\frac{G}{3} J

\frac{G}{4} J

\frac{G}{5} J

\frac{G}{6} J

Hard

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A particle of mass $10 g m$ is kept on the surface of a uniform sphere of mass $100 k g$ and radius $10 c m$ . Find the work done against the gravitational force between them, to take the particle far away from the sphere. $(G = 6.67 \times 1 0^{- 11} N m^{2} / K g^{2})$

3.33 \times 1 0^{- 9} J

3.33 \times 1 0^{- 10} J

6.67 \times 1 0^{- 9} J

6.67 \times 1 0^{- 10} J

Hard

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The work done in shifting a particle of mass $m$ from the centre of earth to the surface of the earth is

- m g R

\frac{1}{2} m g R

z e r o

m g R

Hard

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The work done by an external agent to shift a point mass from infinity to the centre of the earth is W. Then choose the correct relation.

=

W > 0

W < 0

\leq

Hard

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If g is the acceleration due to gravity on the earth's surface, the gain in the potential energy of an object of mass m raised from the surface of the earth to a height equal to the radius R of the earth, is:

2 m g R

\frac{1}{2} m g R

\frac{1}{4} m g R

m g R

Hard

JEE Mains

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A particle hanging from a massless spring stretches it by 2 cm at earths surface. How much will the same particle stretch the spring at a height of 2624 km from the surface of the earth? (Radius of earth $=$ 6400 km).

1 c m

2 c m

3.3 c m

4 c m

Hard

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Gravitation

Physics 2758 Views

A planet in a distant solar system is 10 times more massive than the earth and its radius is 10 times smaller. Given that the escape velocity from the earth is 11km s−1, the escape velocity from the surface ofthe planet would be

At what distance above the surface of earth, the gravitational force will be reduced by 10%, if the radius of earth is 6370 Km.

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

A boy can jump to a height h from ground on earth . What should be the radius of a sphere of density δ such that on jumping on it, he escapes out of the gravitational field of the sphere?

A particle of mass 1kg is placed at a distance of 4m from the centre and on the axis of a uniform ring of mass 5kg and radius 3m. The work done to increase the distance of the particle from 4m to 3​m is.

A particle of mass 10gm is kept on the surface of a uniform sphere of mass 100kg and radius 10cm. Find the work done against the gravitational force between them, to take the particle far away from the sphere. (G=6.67×10−11Nm2/Kg2)

The work done in shifting a particle of mass m from the centre of earth to the surface of the earth is

The work done by an external agent to shift a point mass from infinity to the centre of the earth is W. Then choose the correct relation.

If g is the acceleration due to gravity on the earth's surface, the gain in the potential energy of an object of mass m raised from the surface of the earth to a height equal to the radius R of the earth, is:

A particle hanging from a massless spring stretches it by 2 cm at earths surface. How much will the same particle stretch the spring at a height of 2624 km from the surface of the earth? (Radius of earth = 6400 km).

Physics
2758 Views

A planet in a distant solar system is $10$ times more massive than the earth and its radius is $10$ times smaller. Given that the escape velocity from the earth is $11 k m$ $s^{- 1}$ , the escape velocity from the surface ofthe planet would be

At what distance above the surface of earth, the gravitational force will be reduced by $10 %$ , if the radius of earth is $6370$ Km.

The value of $g$ at a height $h$ above the surface of the earth is the same as at a depth $d$ below the surface of the earth. When both $d$ and $h$ are much smaller than the radius of earth, then which one of the following is correct

A boy can jump to a height $h$ from ground on earth . What should be the radius of a sphere of density $δ$ such that on jumping on it, he escapes out of the gravitational field of the sphere?

A particle of mass 1kg is placed at a distance of 4m from the centre and on the axis of a uniform ring of mass 5kg and radius 3m. The work done to increase the distance of the particle from 4m to $3 m$ is.

A particle of mass $10 g m$ is kept on the surface of a uniform sphere of mass $100 k g$ and radius $10 c m$ . Find the work done against the gravitational force between them, to take the particle far away from the sphere. $(G = 6.67 \times 1 0^{- 11} N m^{2} / K g^{2})$

The work done in shifting a particle of mass $m$ from the centre of earth to the surface of the earth is

A particle hanging from a massless spring stretches it by 2 cm at earths surface. How much will the same particle stretch the spring at a height of 2624 km from the surface of the earth? (Radius of earth $=$ 6400 km).