Q19 of 46 Page 247

What will be the acceleration due to gravity on the surface of the moon, if its radius is 1/4th the radius of the earth and its mass is 1/80 times the mass of the earth.


Where G is the universal gravitational constant( = 6.67 × 10-11 Nm2kg-2),


M is the mass of the earth,


R is the radius of the earth.



(given)


Now



= 9.8× (1/80) × 42


= 1.96 ms-2


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17

Two balls of masses in ratio 2:1 are dropped from the same height. Neglecting air resistance, find the ratio of

(i) the time taken for them to reach the ground.


(ii) the forces acting on them during motion.


(iii) their velocities when they strike the ground.


(iv) their acceleration when they strike the ground.

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An object of mass 1 kg is dropped from a height of 20 m. It hits the ground and rebounds with the same speed. Find the change in momentum. (Take g = 10 m/s2)

 20

A boy weighing 20 kg is sitting at one end of a see-saw at a distance of 1.2 m from the centre. Where should a man weighing 60 kg sit on the see-saw, so that it stands balanced?

 21

A cart driver prods his horse to move forward. The horse refuses to budge and explains:

“According to Newton’s III Law, I am pulling the cart, with a certain force and the cart, in turn pulls me back with an equal amount of force. As they are equal in magnitude and act in opposite directions, they cancel each other.”


Do you agree with the explanation given by the horse? Support your answer with proper reasons.