Force,Density & Pressure

Question 1

Density

Answer 1

Mass per unit volume
P=m/v

Question 2

Volume

Answer 2

Space occupied by molecules of a substance.

Question 3

Volume of sphere

Answer 3

4/3πr^3 or 1/6πd^3

Question 4

Volume of cylinder

Answer 4

πr^2h or πd^2h/4

Question 5

Volume of rectangle

Answer 5

lbh

Question 6

Pressure

Answer 6

Force exerted perpendicularly per unit area.
p=F/A

Question 7

Pressure of liquid

Answer 7

vPg

Question 8

Weight

Answer 8

Amount of gravitational force acting on an object towards the center of gravitational field.

Question 9

Friction

Answer 9

It’s a contact force that opposes motion, which acts at contact area.

Question 10

Drag force

Answer 10

Its an opposing force that acts on object by fluid molecules.

Question 11

Viscous force

Answer 11

Its a frictional force that opposes motion between the surface of the object and the fluid molecules.

Question 12

Upthrust

Answer 12

If an object is immersed in fluid partially or completely, the vertically upward net force is known as upthrust.
U=vpg
volume of object immersed
density of fluid

Question 13

Why does upthrust act on an object?

Answer 13

More depth causes more pressure as pressure is directly proportional to depth. The upward force at the bottom of the object is greater than downward force at the top. So net upward force causes upthrust.

Question 14

Pivot

Answer 14

It is the point at which object can rotate freely

Question 15

Moment

Answer 15

It is the product of force and perpendicular distance between the pivot to the line of action of force.

Question 16

Types of moment?

Answer 16

1. Clockwise moment
2. Anti-clockwise moment

Question 17

Principle of moment

Answer 17

At equilibrium, sum of clockwise moment about any point is equal to sum of anti-clockwise moment about the same point.

Question 18

Centre of mass/gravity

Answer 18

It is the point around which whole weight of object seems to act.

Question 19

Couple

Answer 19

Pair of equal and anti-parallel forces which creates rotational motion not translational motion.

Question 20

Torque

Answer 20

It is the product of one of the forces in couple and perpendicular distance between the pivot to the line of action of couple force.

Question 21

Conditions of equilibrium

Answer 21

1. Net force along any direction =0
2. Net moment about any point =0