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**SHORT ANSWER TYPE QUESTION**

**Q.1. (a) Name the balances used to measure mass and weight. ****(b) Weight of an object will be lessor or more at Antarctica as compared to the weight of object at Delhi. Give reason for your answer. [CBSE 2016]****Ans. **(a) Mass is measured by beam balance. Weight is measured by spring balance.

(b) Earth is flattened at poles. So distance of the body from its centre is less. As hence value of ‘g’ in Antarctica will be more as compared to that in Delhi. Consequently, its weight will be more in Antarctica than in Delhi.**Q.2. Mona weighs 750 N on Earth.****(i) On the planet Mars, the force of gravity is 38% of that of Earth. How will Mona weigh on Mars?****(ii) What will be Mona’s mass on Earth (g = 10 m/s ^{2})? [CBSE 2016]**

∴ Weight on Mars = 0.38 x Weight on Earth

= 0.38 x 750 = 285 N

Mass of Earth =

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If F becomes (F/2), then let distance becomes R'.

i.e. distance is increased √2 times.

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where M

R

Mass of planet = 2M

∴

Weight on plane

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(a) motion of planets around the sun in their orbits.

(b) presence of an atmosphere around the earth.

(b) The density of an object is 1.8 g/cm

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(i) decrease the force acting on the surface, and

(ii) increase the surface area of given surface.

(b) The density of an object in CGS system is d = 1.8 g/cm

∵ 1 g/cm

d = 1.8 x 10

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In present question weight of Ramesh on earth

⇒ Weight of Ramesh on Neptune,

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If suddenly earth shrinks to one-third of its present size without any change in mass then

Hence new value of g will be

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(i) As per relation v = u + at, we have

0 = u + ( - 10) x 3 ⇒ u = + 30 m s

(ii) As per relation v

(0)

(a) Find the distance it falls through in 1 second?

(b) Find the distance it falls through in 3 seconds. Also, find the speed with which it strikes the ground after 3 seconds. [CBSE 2015]

Ans.

(a) Distance h

(b) Distance h through which particle falls in time t = 3 s will be:

and speed with which it reaches the ground after time t = 3 s, will be:

v = u + gt = gt = 9.8 x 3 = 29.4 m s

**Ans.** By law of gravitation, of F ∝ mass

If the distance is increased by a factor of 6, F decreases by 1/36 times.

Thus, mass should be increased by (6)^{2} times i.e. 36 times.

Thus mass also has to be increased.**Q.24. What happens to the magnitude of the force of gravitation between two objects if(i) distance between the objects is tripled?(ii) mass of both objects is doubled?(iii) mass of both objects as well as distance between them is doubled? [CBSE (CCE 2015)]Ans.** (i) If distance is tripled, i.e. R → 3R

By Newtons law,

Thus F becomes (1/3)

(ii) Masses are doubled i.e.

By Newton’s law, F ∝ M

Thus F becomes (2) x (2) = 4 times its original value.

(iii) Masses

Distance

By Newton’s law,

Or

On changing masses and distance,

Thus force remains unchanged.

**LONG ANSWER QUESTIONS**

**Q.1. (a) A body floats in kerosene of density 0.8 x 10 ^{3} kg/m^{3} up to a certain mark. If the same body is placed in water of density 1.0 x 10^{3} kg/m^{3}, will it sink more or less? Give reason for your answer.**(a) The body will sink less in water. When a body of weight W floats on a liquid of density p with a volume V immersed in the liquid, the upthrust must balance the weight and hence

(b) If a fresh egg is put into a beaker filled with water, it sinks. On dissolving a lot of salt in the water the egg begins to rise and then floats. Why? [CBSE 2016]

Ans.

⇒

As density of water (p

(b) A fresh egg put into a beaker filled with water sinks because density of egg is more than the density of water.

When a lot of salt is dissolved in the water, the density of salt solution becomes more than the density of egg. As a result, now the egg starts floating in highly saltish water.**Q.2. (i) State two factors on which the gravitational force between two objects depends.(ii) Why is ‘G’ called a universal constant?(iii) What happens to the gravitational force between two objects if masses of both the objects are doubled and the distance between them is also doubled?(iv) What is the value of ‘G' on moon?(v) What is the value of 'g' on moon? [CBSE 2015]Ans.** (i) The gravitational force between two objects is (a) directly proportional to the product of their mases, and (b) inversely proportional to the square of the distance between them.

(ii) G is called a universal constant because its value never changes under any condition.

(iii) The force remains unchanged.

(iv) Value of G on moon is same as bn earth having a value 6.673 x 10

(v) Value of g on moon is 1/6 that of its value on the earth.

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