Unit 1.1 Basic physics

Question 1

What are the 6 essential base SI units and the quantity they measure?

Answer 1

Quantity- Mass(m) SI unit- Kilogram(kg)
Quantity-length(l) SI unit- metre(m)
Quantity-time(t) SI unit- second(s)
Quantity-electric current(l) SI unit- ampere(A)
Quantity-temperature(T) SI unit- kelvin(K)
Quantity-amount of substance(n) SI unit- mole(mol)

Question 2

Alternative units of length and volume

Answer 2

LENGTH
1 kilometre(km) = 1,000m
1 centimetre(cm) = 0.01m
1 millimetre(mm) = 0.001m
1 micrometre(μm) = 0.000 001m
1 nanometre(nm) = 0.000 000 001m

VOLUME
Cubic metre (m3)
1 cubic centimetre(cm3) = 0.000 001m3
1 cubic decimetre(dm3) = 0.001m3
1 litre(l) = 1 cubic decimetre (dm3)
1 millilitre(ml) = 1 cubic centimetre (cm3)

Question 3

The drag force Fd on a sphere moving through a fluid is given by stokes formula Fd = 6πηav where a is the radius of the sphere, v the velocity and n[eta] is the coefficient of viscosity of the fluid. Find the unit of n in terms of the base SI units.

Answer 3

(Some physicists work with quantities other then the base quantities such as area, volume, pressure, power. They use the base units in combination to express these. To derive these units we treat them as algebraic letters.)

Rearranging the equation n= Fd/ 6πηav 6 and π have no units(m,kg, etc.) so [n] = Fd/av
[Fd] = kg m s-2 as it Force(N) = kg m s-2 and Fd in question is a drag force. [a] = m [v] = m s-1 as velocity - m s-1.

So [n] = kg m s-2/m2 s-1 = kg m-1 s-1

Question 4

How can Newton’s(unit of force) be expressed in base si units

Answer 4

N = kg m s-2

Question 5

How can Joules(unit of energy or work) be expressed in base si units

Answer 5

J = kg m2 s-2 (just a side note: in all of the above and below the numbers should be to the power of(just don’t know how to do it on keyboard).

Question 6

How can Watts(unit of power) be expressed in base si units

Answer 6

W = kg m2 s-3

Question 7

Force =
Work =
Power =
(fill in the equations)(Hint: these equations can help express derived units in terms of the base SI units)

Answer 7

Force = mass x acceleration
Work = Force x distance
Power = work/time

Question 8

Derive the Si units of energy

Answer 8

Kinetic energy = 1/2 * mass * velocity2
Units = kg * (m/s) * (m/s)
=kg m2 s-2

Question 9

Express 60TΩ in standard form

Answer 9

6x10^13 (T is tera which = 10^12)

Question 10

write 0.000003m with a suitable prefix

Answer 10

3μm

Question 11

what is the actual value of 8MΩ

Answer 11

8,000,000Ω or 8x10^6Ω

Question 12

What is meant by a scalar quantity

Answer 12

A quantity that only has magnitude

Question 13

What is a vector quantity

Answer 13

A quantity that has magnitude as well as direction

Question 14

Is acceleration a vector or scalar quantity

Answer 14

Vector

Question 15

Is mass a scalar or vector quantity

Answer 15

scalar

Question 16

What is a homogeneity equation

Answer 16

The SI units on one side of the equation must be exactly the same as the other

Question 17

What is a collinear vector

Answer 17

Vectors that are parallel to the same line

Question 18

What are coplanar vectors

Answer 18

Vectors that are only parallel to the same plane (look up an image of coplanar vectors to help you understand)

Question 19

Adding coplanar vectors:
Example: A boat is crossing a river at 1ms^-1. Whilst the river is flowing at 2ms^-1. What is the boats velocity?

Answer 19

First you use the head to tail method. The two vectors we have are the 1ms^-1 going forward and the 2ms^-1 going right. So we first draw the 1ms^-1 line vertically and then we draw the 2ms^-1 above it horizontally creating half a triangle without the bottom. Then we add in the bottom line which is the resultant velocity(Z)and then we add an angle into the triangle which is called angle theta.

To first find the magnitude we use Pythagoras theorem:
Z = √x^2 + y^2
= √2^2 + 1^2
=√5
=2.24 ms^-1

Then to find the direction we use trigonometry and we use tan theta(θ):
tanθ = 2/1
θ =63.4 degrees

Question 20

How do you subtract vectors

Answer 20

(check pmt education unit 1.1 basic physics part on subtracting vectors to see diagram)
To find the vector c = a - b, we can treat this as c = a + (-b). The negative of a vector has the same magnitude but a reversed direction.

Question 21

How do you resolve vectors into two components

Answer 21

Vectors acting at an angle can be resolved into horizontal and vertical components. To resolve a vector into these two perpendicular components you need a set of perpendicular coordinate axes such as the simple x-y axes in a cartesian coordinate system

Question 22

What is the equation used to calculate density

Answer 22

p = m/v
Density = Mass/Volume
Density units: kg m^-3
Mass units: kg
Volume units: m^3

Question 23

What is a moment

Answer 23

A moment is the turning effect of a force. It is a composition of the distance away from the pivot and the magnitude of the force applied.

Question 24

The principle of moments

Answer 24

Principle of moment states that for a body to be in equilibrium, the sum of clockwise moments about a pivot should be equal to the sum of anticlockwise moments about the same pivot.
(clockwise is usually the moments on the right of the pivot and the anticlockwise on the left of the pivot)
(IF YOU STILL UNSURE OR DONT REMEMBER LOOK AT http://www.excelatphysics.com/principle-of-moment.html)

Question 25

What are the two equations to work out a moment of a force

Answer 25

moment = force x perpendicular distance from a pivot
moment = perpendicular force x distance from a pivot
M = Fd

Question 26

what is the centre of gravity

Answer 26

The point on a object at which we can model all the weight of the object to act through.

Question 27

if an object is in equilibrium the sum of the anticlockwise moments would be?

Answer 27

Equal to the sum of the clockwise moments

Question 28

What does it mean when an object is in equilibrium

Answer 28

It is not accelerating. Its stationary or Moving at a constant velocity.
(resultant force is 0)
(net moment(sum of the moments acting on the object)is 0)

Question 29

how do you check equations for homogeneity using units?

Answer 29

The units on either side of the equation should be the same.
To check the homogeneity of equations -
-Check the units on both sides of the equation.
-Determine if they are equal.
-If they do not match the equation will need to be adjusted.