Science (English Medium) Class 11 - CBSE Question Bank Solutions for Physics

If the sun and the planets carried huge amounts of opposite charges ______.

1. all three of Kepler’s laws would still be valid.
2. only the third law will be valid.
3. the second law will not change.
4. the first law will still be valid.

Supposing Newton’s law of gravitation for gravitation forces F₁ and F₂ between two masses m₁ and m₂ at positions r₁ and r₂ read F₁ = – F₂ = `- r_12/r_12^3 GM_0^2 ((m_1m_2)/M_0^2)^n` where M₀ is a constant of dimension of mass r₁₂ = r₁ – r₂ and n is a number. in such a case.

1. the acceleration due to gravity on earth will be different for different objects.
2. none of the three laws of Kepler will be valid.
3. only the third law will become invalid.
4. for n negative, an object lighter than water will sink in water.

The centre of mass of an extended body on the surface of the earth and its centre of gravity ______.

1. are always at the same point for any size of the body.
2. are always at the same point only for spherical bodies.
3. can never be at the same point.
4. is close to each other for objects, say of sizes less than 100 m.
5. both can change if the object is taken deep inside the earth.

Give one example each of central force and non-central force.

Draw areal velocity versus time graph for mars.

What is the direction of areal velocity of the earth around the sun?

Out of aphelion and perihelion, where is the speed of the earth more and why?

A star like the sun has several bodies moving around it at different distances. Consider that all of them are moving in circular orbits. Let r be the distance of the body from the centre of the star and let its linear velocity be v, angular velocity ω, kinetic energy K, gravitational potential energy U, total energy E and angular momentum l. As the radius r of the orbit increases, determine which of the above quantities increase and which ones decrease.

Earth’s orbit is an ellipse with eccentricity 0.0167. Thus, earth’s distance from the sun and speed as it moves around the sun varies from day to day. This means that the length of the solar day is not constant through the year. Assume that earth’s spin axis is normal to its orbital plane and find out the length of the shortest and the longest day. A day should be taken from noon to noon. Does this explain variation of length of the day during the year?

A satellite is in an elliptic orbit around the earth with aphelion of 6R and perihelion of 2 R where R= 6400 km is the radius of the earth. Find eccentricity of the orbit. Find the velocity of the satellite at apogee and perigee. What should be done if this satellite has to be transferred to a circular orbit of radius 6R ?

[G = 6.67 × 10^–11 SI units and M = 6 × 10²⁴ kg]

Pressure is a scalar quantity because ______.

1. it is the ratio of force to area and both force and area are vectors.
2. it is the ratio of the magnitude of the force to area.
3. it is the ratio of the component of the force normal to the area.
4. it does not depend on the size of the area chosen.

Iceberg floats in water with part of it submerged. What is the fraction of the volume of iceberg submerged if the density of ice is ρ_i = 0.917 g cm^–3?

A vessel filled with water is kept on a weighing pan and the scale adjusted to zero. A block of mass M and density ρ is suspended by a massless spring of spring constant k. This block is submerged inside into the water in the vessel. What is the reading of the scale?

The equation of motion of a particle is x = a cos (αt)². The motion is ______.

The displacement time graph of a particle executing S.H.M. is shown in figure. Which of the following statement is/are true?

1. The force is zero at `t = (T)/4`.
2. The acceleration is maximum at `t = (4T)/4`.
3. The velocity is maximum at `t = T/4`.
4. The P.E. is equal to K.E. of oscillation at `t = T/2`.

What are the two basic characteristics of a simple harmonic motion?

Show that the motion of a particle represented by y = sin ωt – cos ωt is simple harmonic with a period of 2π/ω.

A person normally weighing 50 kg stands on a massless platform which oscillates up and down harmonically at a frequency of 2.0 s^–1 and an amplitude 5.0 cm. A weighing machine on the platform gives the persons weight against time.

1. Will there be any change in weight of the body, during the oscillation?
2. If answer to part (a) is yes, what will be the maximum and minimum reading in the machine and at which position?

A person normally weighing 50 kg stands on a massless platform which oscillates up and down harmonically at a frequency of 2.0 s^–1 and an amplitude 5.0 cm. A weighing machine on the platform gives the persons weight against time.

1. Will there be any change in weight of the body, during the oscillation?
2. If answer to part (a) is yes, what will be the maximum and minimum reading in the machine and at which position?

The sign of work done by a force on a body is important to understand. State carefully if the following quantity is positive or negative:

Work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket.