NCERT Class 11 Physics Solutions: Chapter 8 – Gravitation-Part 4

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Question 8.9:

Which of the following symptoms is likely to afflict an astronaut in space

(a) Swollen feet,

(b) Swollen face,

(c) Headache,

(d) Orientation problem?

Answer:

, and

Explanation:

symptoms is likely to afflict an astronaut in space shown in …

Symptoms is Likely to Afflict an Astronaut in Space

Swollen feet:

Legs hold the entire mass of a body in standing position due to gravitational pull. In space, an astronaut feels weightlessness because of the absence of gravity. Therefore, swollen feet of an astronaut do not affect him/her in space.

Swollen face:

A swollen face is caused generally because of apparent weightlessness in space. Sense organs such as eyes, ears nose, and mouth constitute a person’s face. This symptom can affect an astronaut in space.

Headache:

Headaches are caused because of mental strain. It can affect the working of an astronaut in space.

Orientation problem:

Space has different orientations. Therefore, orientation problem can affect an astronaut in space.

Question 8.10:

Choose the correct answer from among the given ones: The gravitational intensity at the centre of a hemispherical shell of uniform mass density has the direction indicated by the arrow shown in figure.

The gravitational intensity at the centre of a hemispherical …

Figure Shown the Direction Indicated by the Arrow

Answer:

Explanation:

Gravitational potential is constant at all points in a spherical shell. Hence, the gravitational potential gradient is zero everywhere inside the spherical shell. The gravitational potential gradient is equal to the negative of gravitational intensity. Hence, intensity is also zero at all points inside the spherical shell. This indicates that gravitational forces acting at a point in a spherical shell are symmetric.

If the upper half of a spherical shell is cut out (as shown in the given figure), then the net gravitational force acting on a particle located at centre will be in the downward direction.

If the upper half of a spherical shell is cut out (as shown …

Gravitational Force Acting on a Particle Located at Centre

Since gravitational intensity at point is defined as the gravitational force per unit mass at that point, it will also act in the downward direction. Thus, the gravitational intensity at centre O of the given hemispherical shell has the direction as indicated by arrow .

Question 8.11:

Choose the correct answer from among the given ones: For the problem , the direction of the gravitational intensity at an arbitrary point is indicated by the arrow

Answer:

Explanation:

Gravitational potential is constant at all points in a spherical shell. Hence, the gravitational potential gradient is zero everywhere inside the spherical shell. The gravitational potential gradient is equal to the negative of gravitational intensity. Hence, intensity is also zero at all points inside the spherical shell. This indicates that gravitational forces acting at a point in a spherical shell are symmetric.

If the upper half of a spherical shell is cut out (as shown in the given figure), then the net gravitational force acting on a particle at an arbitrary point P will be in the downward direction.

If the upper half of a spherical shell is cut out , then the …

Gravitational Force Acting on a Particle at an Arbitrary Poi …

Since gravitational intensity at a point is defined as the gravitational force per unit mass at that point, it will also act in the downward direction. Thus, the gravitational intensity at an arbitrary point of the hemispherical shell has the direction as indicated by arrow.