Forces

Question 1

Hooke’s law

Answer 1

magnitude of force F exerted by a spring on a body attached to the spring is proportional to the extension x of the spring from equilibrium provided the limit of proportionality of the spring is not exceeded

Question 2

formula of force exerted on a spring

Answer 2

F =kx
F load/force applied to the material [N]
k spring constant/restoring force constant [N m-¹]
x extension/compression of the spring [m]

Question 3

formula for elastic potential energy

Answer 3

Work done by F in stretching/compressing spring = 1/2 k x²

elastic potential energy stored = area under F-x graph

Question 4

spring in series and parallel

Answer 4

series: total extension is doubled

parallel : each spring F is halved

Question 5

pressure is defined as force per unit area

Answer 5

P= F/A
P pressure applied [Pa or N m-²]
F load /force applied
A area of object in contact with the surface [m²]

Question 6

Pressure due to Fluid at a point

Answer 6

p =hρg
h vertical depth from surface of the liquid
ρ density of fluid
g gravitational acceleration

Question 7

total pressure on fluid at depth h

Answer 7

Ptotal = Patm + Pfluid

Question 8

Upthrust acting on an object in a fluid

Answer 8

net upward force exerted by the fluid due to the pressure difference on the upper and lower surface areas of the object

Question 9

net vertical fluid force , Upthrust U

Answer 9

U= Ρfluid Vfluid displaced g
= Mfluid displaced g
= Wfluid displaced

Question 10

Archimedes Principle ( calculation of upthrust)

Answer 10

the upthrust acting on a body, partially or totally immersed in a fluid is equal to the weight of the fluid displaced by the body

Question 11

Law of flotation U=Wobject

Answer 11

when an object floats in equilibrium, the weight of the fluid displaced by the object ( i.e. upthrust) equals the weight of that object

Question 12

centre of gravity of an object

Answer 12

point through which the entire weight of a body acts

Question 13

Moment of a force ( torque of force) about a point

Answer 13

turning effect of the force about that point and is equal to the product of that force and the perpendicular distance from its line of action to that point

Question 14

moment of F about O

Answer 14

τ about o = F × d
τ about o turning moment [N m]
F magnitude of the force [N]
d perpendicular distance from the line of action of the force to the axis [m]

Question 15

A couple

Answer 15

a pair of force of equal magnitude but opposite in direction acting on an object where their lines of action do not coincide producing only rotation

Question 16

torque of a couple

τ couple = F d perpendicular

Answer 16

product of one of the forces and the perpendicular distance between the line of action of the force

Question 17

conditions for an object to be in equilibrium

Answer 17

1. no resultant force in any direction ΣFx=0 ΣFy=0

2. no resultant torque Στ=0

Question 18

Translational equilibrium

Answer 18

Newton’s first law
every object remains in its state of rest or move with uniform speed in a straight line unless a resultant external force acts on it

Question 19

Rotational equilibrium

Answer 19

principle of moments
for an object to be in rotational equilibrium, the sum of clockwise moments about any pivot must equal the sum of anti clockwise moments about that pivot