Forces

Question 1

State Hooke’s Law.

Answer 1

Hooke’s Law states that the extension of a spring is
proportional to the applied force if the limit of proportionality is not exceeded.
F = kx

Question 2

Using the definitions of pressure and density, derive the formula of fluid pressure P = pgh, where p = density of fluid, g = gravitational field strength, h = depth of fluid

Answer 2

P = force/area
= weight of liquid/A
= mg/A
= pVg/A
= p(Ah)g/A
= pgh

Question 3

Define upthrust.

Answer 3

Upthrust is the net upward force exerted by a fluid on an object submerged fully or partially in the fluid due to the difference in pressure exerted by the fluid on the upper and lower surfaces of the object.
U = pVg = mg
all values above correspond to the liquid where the object is submerged in

Question 4

State Archimedes’ Principle.

Answer 4

For a body submerged or floating in a fluid, the upthrust acting on the body is equal in magnitude and opposite in direction to the weight of fluid displaced by the body.

Question 5

Define an object’s centre of gravity.

Answer 5

It is an imaginary point where all the weight of the object seems to act on.

Question 6

Define the moment of a force.

Answer 6

The moment of a force about a point is the product of the force and the perpendicular distance of the line of action of the force to the point.
τ = Fd sin θ

Question 7

Define a couple and its torque.

Answer 7

A couple is a pair of forces, which equal in magnitude but opposite in direction, whose lines of action do
not coincide.

The torque due a couple is defined as the product of one of the forces and the perpendicular
distance between the forces

Question 8

Define static equilibrium.

Answer 8

Static equilibrium is when the net external force acting on the body is 0 and the net moment
on the body about any point is zero.

Question 9

State the Principle of moments.

Answer 9

The Principle of Moments states that when a body is in equilibrium, the sum of clockwise moments about any point must be equal to the sum of anticlockwise moments about the same point.

Question 10

Define apparent weight.

Answer 10

Apparent weight is given by the normal contact force acting on an object.