Gravitation Worksheet13

Name these forces :
(a) the upward push of water on a submerged object
(b) the force which wears away two surfaces as they move over one another
(c) the force which pulled the apple off Isaac Newton’s tree.
(d) the force which stops you falling through the floor.

A pressure of 10 Pa acts on an area of 3.0 m^{2}. What is the force acting on the area? What force will be exerted by the application of same pressure if the area is made onethird ?

Aarushi is wearing a pair of flat shoes. She weighs 550 N. the area of contact of one shoe with the ground is 160 cm^{2}. What pressure will be exerted by her on the ground :
(a) if she stands on two feet?
(b) if she stands on one foot?

Calculate the density of an object of volume 3 m^{3} and mass 9 kg. State whether this object will float or sink in water. Give reason for your answer.

An object weighs 500 grams in air. This object is then fully immersed in water. State whether it will weigh less in water or more in water. Give reason for your answer.

(a) Write down an equation that defines density.
(b) 5 kg of material A occupy 20 cm^{3} whereas 20 kg of material B occupy 90 cm^{3}. Which has the greater density : A or B ? Support your answer with calculations.

(a) Define buoyant force. Name two factors on which buoyant force depends.
(b) What is the cause of buoyant force?
(c) When a boat is partially immersed in water, it displaces 600 kg of water. How much is the buoyant force acting on the boat in newtons ? (g = 10 m s^{–2})

A floating boat displaces water weighing 6000 newtons.
(i) what is the buoyant force on the boat?
(ii) what is the weight of the boat?

The density of turpentine is 840 kg/m^{3}. What will be its relative density? (Density of water = 1000 kg/ m^{3})

Calculate the pressure when a force of 200 N is exerted on an area of : (i) 10 m^{2}
Answer:

(a) Buoyant force (b) Force of friction
(c) Gravitational force (d) Reaction (force)

30 N ; 10 N

(a) 17187.5 N/ m^{2} , (b) 34375 N/ m^{2}

3 kg/ m^{3}; Float in water ; Because the density of object is less than the density of water

It will weigh less in water; Because an upward force (buoyant force) equal to the weight of water displaced acts on the object when immersed in water which reduces its apparent weight

(a) A substance is defined as mass of the substance per unit volume.
(b) A

The tendency of a liquid to exert an upward force on an object placed in it, is called buoyancy.
The magnitude of buoyant force acting on an object immersed in a liquid depends on two factors:
(i) Volume of object immersed in the liquid, and (ii) Density of the liquid.
Every liquid and even the gases exhibit the property of buoyancy
(c) 6000 N

(i) 6000 N (ii) 6000 N

0.84

20 Pa