class 9 chapter-- Gravitation

 

Class-IX                   CH. GRAVITATION

 

Q1. Why are sleepers laid down under the train tracks?

Q2. Why do trucks have wide tyres?

Q3. Why do needles have sharp tips?

Q4. Why is it painful to walk barefoot on small pebbles?

Q5. A cubical block of edge 2cm and of mass 5kg is kept on a table top. Calculate the thrust and the pressure of the block on the table top. (Thrust=49N and P=1.225 X 10⁵ Pa)

Q6. A wooden block of mass 8 kg & of dimension 40 cm x 30 cm x 20 cm is kept on a tabletop. Find the pressure exerted by the wooden block on the table top if it is made to lie on the tabletop with its side of dimension   a) 40 cm x 30 cm b) 30 cm x 20 cm.  Find the ratio of greatest & least pressure on the table top.(Ans. P_g : P_l= 2:1)

Q7. A boy weighing 60 Kg has shoes with heel of area of cross-section 15 cm² while a girl weighing 45 Kg is wearing shoes with heel of area of cross-section 2.0 cm². Compare the pressure exerted on ground by their heels when they stand on two foot. (P₁: P₂ =8 : 45)

Q8. Give reason: a) The blood pressure in humans is greater at the feet than the brain.

b) Camels can walk easily in the desert.

c) The wall of a dam is made broader at its base.

Q9. Why does a mug full of water feel lighter inside water?

Q10.  If an egg is put in beaker, it sinks. On dissolving a lot of salt in the water the egg begins to rise and then floats. Why?

Q11. If a wooden block and an iron block of same volume are immersed in a liquid, will they experience the same weight loss? Why?

Q12. A wooden boat displaces water equal to 5000N. Find the buoyant force and mass of the boat.

Q13. A solid body of volume 60cm³ is fully immersed in water. Calculate the buoyant force.

Q14. An object is immersed in different liquids. Does same buoyant force acts on the object due to all the liquids?

Q15. Why does a block of wood held under water rise when released?

Q16. Calculate the density of water if it has a mass of 1160 Kg and a volume of 1 m³.

Q17. If you find a shiny rock, a carbon allotrope with a volume of 0.042 cm³ and a mass of 0.14 g, is it graphite or diamond? The density of graphite is 2.266 g/cm³ and the density of diamond is 3.51g/cm³.