M3C2

Question 1

Define resultant force

Answer 1

A single force which has the same effect as the sum of all forces acting on a body

Question 2

Define a Newton

Answer 2

The force required to accelerate 1 Kg by 1 m s^-1

units = N (Kg m s^-2)

Question 3

What’s the formula for force?

Answer 3

Force (N) = Mass (kg) x Acceleration (m s^-2)

F=MA

Question 4

Define weight

Answer 4

The force a body exerts when in the presence of a gravitational field (w=mg)

Question 5

Define tension

Answer 5

The force experienced by a rope, cable, string or wire that is being pulled, hung, rotated or supported in any fashion

Question 6

A ball, of mass 1 kg, is being hung in the air but a string. What is the tension in the string?

Answer 6

Tension is equal to the force being exerted on it, so in this case weight of the ball
t = m x g
t = 9.81 N

Question 7

Define normal contact force

Answer 7

A force that acts perpendicular to the point of contact of a body against a surface. It’s sometimes called the reaction force.

Question 8

A block of mass ‘m’ is place in contact with a flat table. What is the magnitude of the normal contact force?

Answer 8

In this case,

R = mg

Question 9

A block of mass ‘m’ is place in contact with a slanted table table at angle θ to the horizontal. What is the magnitude of the normal contact force?

Answer 9

In this case,
R = mg cos(θ)

(See M3C2L2 for diagram)

Question 10

Define fluid

Answer 10

A substance that has no fixed shape and yields easily to pressure

Question 11

What is the Drag equation?

Answer 11

F(drag) = 1/2 ρC(drag)AV^2
F(drag) = Drag force (N)
ρ = Density of the fluid (kg m^-3)
C(drag) = Drag coefficient
A = Cross sectional area of the moving object (m^2)
V = Velocity (m s^-1)

Question 12

What is terminal velocity?

Answer 12

Terminal velocity is when the force of gravity (downwards force) is equal to the drag force (upwards force)

Question 13

Define Equilibrium

Answer 13

If the resultant force acting an object is 0 it’s said to be in equilibrium.
This can occur in two situations;
- When the object isn’t moving
- When there is no change in motion (constant velocity)

Question 14

Define a couple

Answer 14

Two equal, anti-parallel forces acting to produce rotation (no linear motion)

Question 15

Define torque

Answer 15

The moment or turning effect produced by a couple

Question 16

What’s the formula for working out a moment?

Answer 16

Moment (Nm) = Force (N) x Perpendicular distance from pivot (m)

Question 17

What’s the principle of moments?

Answer 17

Σ anticlockwise moment = Σ clockwise moment

In this case the object is in equilibrium

Question 18

There is a 15 N force acting at the end of a plank 4 m long. What is the magnitude of the moment?

Answer 18

15 N x 4 m = 60 Nm

Question 19

Define center of mass (CoM)

Answer 19

The single point at which all of an objects mass can be assumed to be situated.
The center of mass can act as a pivot

Question 20

Define density

Answer 20

The mass per unit volume of a substence

Question 21

What’s the equation for density?

Answer 21

ρ = m / v
ρ = density (kg m^-3)
m = mass (kg)
v = volume (m^-3)

Question 22

What’s the volume of a cone?

Answer 22

V=πr^2h/3

Question 23

What’s the formula for pressure?

Answer 23

P = F/A
P = Pressure (Pa)
F = Force (N)
A = Area (m^2)

Question 24

What’s the pressure if a 20 N is acting over 4 m^2?

Answer 24

20 N / 4 m = 5 Pa

Question 25

What’s the formula for hydro-static pressure?

Answer 25

P = h ρ g
P = Pressure (Pa)
h = height (m)
ρ = Density (kg m^-3)
g = acceleration due to gravity (m s^-2)