Science (English Medium) इयत्ता ११ - CBSE Question Bank Solutions

The velocity of a body of mass 2 kg as a function of t is given by `v(t) = 2t  hati + t^2hatj`. Find the momentum and the force acting on it, at time t = 2s.

 A cricket bowler releases the ball in two different ways

1. giving it only horizontal velocity, and
2. giving it horizontal velocity and a small downward velocity. The speed v_s at the time of release is the same. Both are released at a height H from the ground. Which one will have greater speed when the ball hits the ground? Neglect air resistance.

An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. This is because ______.

A man, of mass m, standing at the bottom of the staircase, of height L climbs it and stands at its top.

1. Work done by all forces on man is equal to the rise in potential energy mgL.
2. Work done by all forces on man is zero.
3. Work done by the gravitational force on man is mgL.
4. The reaction force from a step does not do work because the point of application of the force does not move while the force exists.

A bullet of mass m fired at 30° to the horizontal leaves the barrel of the gun with a velocity v. The bullet hits a soft target at a height h above the ground while it is moving downward and emerges out with half the kinetic energy it had before hitting the target.

Which of the following statements are correct in respect of bullet after it emerges out of the target?

1. The velocity of the bullet will be reduced to half its initial value.
2. The velocity of the bullet will be more than half of its earlier velocity.
3. The bullet will continue to move along the same parabolic path.
4. The bullet will move in a different parabolic path.
5. The bullet will fall vertically downward after hitting the target.
6. The internal energy of the particles of the target will increase.

Give example of a situation in which an applied force does not result in a change in kinetic energy.

Two bodies of unequal mass are moving in the same direction with equal kinetic energy. The two bodies are brought to rest by applying retarding force of same magnitude. How would the distance moved by them before coming to rest compare?

A raindrop of mass 1.00 g falling from a height of 1 km hits the ground with a speed of 50 ms^–1. Calculate 

1. the loss of P.E. of the drop.
2. the gain in K.E. of the drop.
3. Is the gain in K.E. equal to a loss of P.E.? If not why.

Take g = 10 ms^–2

Suppose the average mass of raindrops is 3.0 × 10^–5 kg and their average terminal velocity 9 ms^–1. Calculate the energy transferred by rain to each square metre of the surface at a place which receives 100 cm of rain in a year.

A rocket accelerates straight up by ejecting gas downwards. In a small time interval ∆t, it ejects a gas of mass ∆m at a relative speed u. Calculate KE of the entire system at t + ∆t and t and show that the device that ejects gas does work = `(1/2)∆m u^2` in this time interval (neglect gravity).

As observed from earth, the sun appears to move in an approximate circular orbit. For the motion of another planet like mercury as observed from earth, this would ______.

Different points in earth are at slightly different distances from the sun and hence experience different forces due to gravitation. For a rigid body, we know that if various forces act at various points in it, the resultant motion is as if a net force acts on the c.m. (centre of mass) causing translation and a net torque at the c.m. causing rotation around an axis through the c.m. For the earth-sun system (approximating the earth as a uniform density sphere).

Choose the wrong option.

Particles of masses 2M, m and M are respectively at points A, B and C with AB = ½ (BC). m is much-much smaller than M and at time t = 0, they are all at rest (Figure). At subsequent times before any collision takes place ______.

If the law of gravitation, instead of being inverse-square law, becomes an inverse-cube law- ______.

1. planets will not have elliptic orbits.
2. circular orbits of planets is not possible.
3. projectile motion of a stone thrown by hand on the surface of the earth will be approximately parabolic.
4. there will be no gravitational force inside a spherical shell of uniform density.

Molecules in air in the atmosphere are attracted by gravitational force of the earth. Explain why all of them do not fall into the earth just like an apple falling from a tree.

How is the gravitational force between two point masses affected when they are dipped in water keeping the separation between them the same?

We can shield a charge from electric fields by putting it inside a hollow conductor. Can we shield a body from the gravitational influence of nearby matter by putting it inside a hollow sphere or by some other means?

The gravitational force between a hollow spherical shell (of radius R and uniform density) and a point mass is F. Show the nature of F vs r graph where r is the distance of the point from the centre of the hollow spherical shell of uniform density.

The gravitational force between a hollow spherical shell (of radius R and uniform density) and a point mass is F. Show the nature of F vs r graph where r is the distance of the point from the centre of the hollow spherical shell of uniform density.