Total marks – 40 Time – 2 Hrs.

**Q 1 (A) Choose the correct alternatives ( 5 marks) GRAVITATION TEST**

- If the distance between two objects increases 5 times, the gravitational force becomes times.

(a) 5

(b) 15

(c) 1/25

(d) 25

- The gravitational force on the surface of the Moon is times than that on the surface of the Earth.

(a) five

(b) one fifth

(c) one sixth

(d) six

- According to Newton’s first law, if mass is more, then the inertia of the body is.

(a) less

(b) very less

(c) more

(d) can’t say

- The weight of body gradually decreases from.

(a) equator to poles

(b) poles to equator

(c) pole to pole

(d) height to surface

- A body of mass 1 kg is attracted by the Earth with a force which is equal to.

(a) 9.8 N

(b) 6.67 × 10^{-11}

(c) 1 N

(d) 9.8 m/s

GRAVITATION TEST

**(B) Answer the following ( 5 marks)**

- Fill in the blank. SI unit of G is …..
- Gravitational waves are detected by…
- Find the odd word out: Acceleration, mass, force, weight
- Kinetic energy: 1 /2 mv
^{2}: Gravitational Potential energy: … - State whether the following statements are True or False. Correct the false statement. Force = mass × velocity

**Q 2 (A) Give scientific reasons (Any 2) (4Marks)**

- In the spacecraft, travellers and objects appear floating
- Weight of an object changes from place to place on the surface of the Earth.
- The value of 1 kg gold weigh different at pole and equator

**(B) Answer the following (Any 3) (6 Marks)**

- Distinguish between mass and weight.
- Define – free fall, Centripetal force
- The value of ‘g’ at the centre of the Earth is zero. Explain?
- Mahendra and Virat are sitting at a distance of 1 metre from each other. Their masses are 75 kg and 80 kg respectively. What is the gravitational force between them?
- Let the period of revolution of a planet at a distance 2R from a star be T. Prove that if it was at a distance of 8 R from the star, its period of revolution will be 8 T.

GRAVITATION TEST

**Q.3 Answer the following (Any five) (15Marks)**

### 1.What happens to the gravitational force between two objects, if –

- the mass of the object is doubled
- the distance between the objects is doubled
- the mass of both objects are doubled and the distance between them is quadrupled.(4 times)

### 2. A ball is thrown vertically upwards with a velocity of 49 m/s. calculate –

- the maximum height to which it rises
- the total time it takes to return to the earth surface.

### 3. Define: The Universal law of gravitation and derive mathematically.

### 4. Observe the figure and answer the following questions:

GRAVITATION TEST

- Write gravitational force between them.
- What will happen to gravitational force if mass of one of the objects is doubled?
- What is the value of universal constant in SI system?

### 5 . Read the paragraph and answer the questions given below.

Space travellers as well as objects in the spacecraft appear to be floating. Why does this happen? Though the spacecraft is at a height from the surface of the earth, the value of g there is not zero. In the space station the value of g is only 11% less than its value on the surface of the earth. Thus, the height of a spacecraft is not the reason for their weightlessness. Their weightlessness is caused by their being in the state of free fall. Though the spacecraft is not falling on the earth because of its velocity along the orbit, the only force acting on it is the gravitational force of the earth and therefore it is in a free fall state. As the velocity of free fall does not depend on the properties of an object, the velocity of free fall is the same for the spacecraft, the travellers and the objects in the craft. Thus, if a traveller releases an object from her hand, it will remain stationary with respect to her and will appear to be weightless.

- Is the value of g zero in the space station
- Why is weightlessness caused in a spacecraft?
- Why doesn’t the spacecraft fall towards the Earth?

Answer the following questions

- Will the velocity of a stone thrown vertically upwards remain constant or will it change with time? How will it change?
- Why doesn’t the stone move up all the time? Why does it fall down after reaching a certain height?
- What does its maximum height depend on?

### 7. Define: Escape velocity and derive mathematically.

### 8.Explain the three laws given by Kepler

** 4 Answer the following ( Any one) ( 5 Marks)**

- Define acceleration due to gravity(g) and derive an expression for it. State and explain any two factors which affect the acceleration due to gravity.
- Define/write the laws

- Force
- Universal constant of gravitation
- free fall
- Uniform circular motion
- Mass