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

In an experiment to estimate the size of a molecule of oleic acid 1 mL of oleic acid is dissolved in 19 mL of alcohol. Then 1 mL of this solution is diluted to 20 mL by adding alcohol. Now 1 drop of this diluted solution is placed on water in a shallow trough. The solution spreads over the surface of water forming one molecule thick layer. Now, lycopodium powder is sprinkled evenly over the film and its diameter is measured. Knowing the volume of the drop and area of the film we can calculate the thickness of the film which will give us the size of oleic acid molecule.

Read the passage carefully and answer the following questions:

1. Why do we dissolve oleic acid in alcohol?
2. What is the role of lycopodium powder?
3. What would be the volume of oleic acid in each mL of solution prepared?
4. How will you calculate the volume of n drops of this solution of oleic acid?
5. What will be the volume of oleic acid in one drop of this solution?

How many astronomical units (A.U.) make 1 parsec?

Consider a sunlike star at a distance of 2 parsecs. When it is seen through a telescope with 100 magnification, what should be the angular size of the star? Sun appears to be (1/2)° from the earth. Due to atmospheric fluctuations, eye can’t resolve objects smaller than 1 arc minute.

Mars has approximately half of the earth’s diameter. When it is closest to the earth it is at about 1/2 A.U. from the earth. Calculate what size it will appear when seen through the same telescope.

Refer to the graphs in figure. Match the following.

Graph	Characteristic
(a)	(i) has v > 0 and a < 0 throughout.
(b)	(ii) has x > 0 throughout and has a point with v = 0 and a point with a = 0.
(c)	(iii) has a point with zero displacement for t > 0.
(d)	(iv) has v < 0 and a > 0.

A ball is dropped and its displacement vs time graph is as shown figure (displacement x is from ground and all quantities are +ve upwards).

1. Plot qualitatively velocity vs time graph.
2. Plot qualitatively acceleration vs time graph.

A man runs across the roof-top of a tall building and jumps horizontally with the hope of landing on the roof of the next building which is of a lower height than the first. If his speed is 9 m/s, the (horizontal) distance between the two buildings is 10 m and the height difference is 9 m, will he be able to land on the next building? (take g = 10 m/s²)

The velocity-displacement graph of a particle is shown in figure.

1. Write the relation between v and x.
2. Obtain the relation between acceleration and displacement and plot it.

Calculate the work done by a car against gravity in moving along a straight horizontal road. The mass of the car is 400 kg and the distance moved is 2 m.

An adult weighing 600 N raises the centre of gravity of his body by 0.25 m while taking each step of 1 m length in jogging. If he jogs for 6 km, calculate the energy utilised by him in jogging assuming that there is no energy loss due to friction of ground and air. Assuming that the body of the adult is capable of converting 10% of energy intake in the form of food, calculate the energy equivalents of food that would be required to compensate energy utilised for jogging.

A wheel in uniform motion about an axis passing through its centre and perpendicular to its plane is considered to be in mechanical (translational plus rotational) equilibrium because no net external force or torque is required to sustain its motion. However, the particles that constitute the wheel do experience a centripetal acceleration directed towards the centre. How do you reconcile this fact with the wheel being in equilibrium? How would you set a half-wheel into uniform motion about an axis passing through the centre of mass of the wheel and perpendicular to its plane? Will you require external forces to sustain the motion?

A disc of radius R is rotating with an angular speed ωo about a horizontal axis. It is placed on a horizontal table. The coefficient of kinetic friction is µ_k.

1. What was the velocity of its centre of mass before being brought in contact with the table?
2. What happens to the linear velocity of a point on its rim when placed in contact with the table?
3. What happens to the linear speed of the centre of mass when disc is placed in contact with the table?
4. Which force is responsible for the effects in (b) and (c).
5. What condition should be satisfied for rolling to begin?
6. Calculate the time taken for the rolling to begin.

Both earth and moon are subject to the gravitational force of the sun. As observed from the sun, the orbit of the moon ______.

In our solar system, the inter-planetary region has chunks of matter (much smaller in size compared to planets) called asteroids. They ______.

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.

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.