2. Foundations in physics

Question 1

Name the 6 base units (you need to know)

Answer 1

• length / m
• mass / kg
• time / s
• electric current / A
• temperature / K
• amount of substance / mol

Question 2

Write all the prefixes

Answer 2

• peta (P) 15
• tera (T) 12
• giga (G) 9
• mega (M) 6
• kilo (k) 3
• deci (d) -1
• centi (c) -2
• milli (m) -3
• micro (u) -6
• nano (n) -9
• pico (p) -12
• femto (f) -15

Question 3

write down the 12 examples of derived units

Answer 3

• area = m2
• volume = m3
• acceleration =ms-2
• density = kgm-3
• Force (N) = kgms-2
• Pressure (Pa) = Nm-2
• Energy or work done (J) = Nm
• Power (W) = Js-1
• Electric potential difference (V) = JC-1
• Electric resistance (Ω) = VA-1
• Electric charge (C) = As
• Frequency (Hz) = s-1

Question 4

What is a scalar quantity?

Answer 4

A scalar quantity has magnitude (size but not directions)

Question 5

Write down 9 examples of scalar quantities

Answer 5

• length / m
• mass / kg
• time / s
• speed / ms-1
• temperature / K
• volume / m3
• energy / J
• potential difference / V
• power / W

Question 6

What is a vector quantity?

Answer 6

A vector quantity has magnitude and direction

Question 7

Write down 5 examples of vector quantities

Answer 7

• displacement / m
• velocity / ms-1
• acceleration / ms-2
• force / N (kgms-2)
• momentum / kgms-1

Question 8

How do you work out the resultant vector of parallel vectors?

Answer 8

Add them together

Question 9

How do you work out the resultant vector of antiparallel vectors?

Answer 9

1. Make one direction positive and the other negative
2. Add the vectors together

Question 10

How do you work out the resultant vector of two perpendicular vectors?

Answer 10

1. Top and tail the vectors
2. Draw a resultant force line
3. Use pythagoras’ theorem

Question 11

How do you work out the resultant vector of non-perpendicular vectors?

Answer 11

1. Top and tail the vector lines
2. Use cosine or sine rule to find what you need

Question 12

How do you subtract vectors?

Answer 12

1. Swap the direction of one of the vectors
2. Find the resultant force (of the triangle)

Question 13

What are the equations for resolving vectors?

Answer 13

Fx = Fcosø
Fy = Fsinø

(where ø is the angle made with the x direction)

Question 14

QUESTION:

There is a force of 5.0N acting at 60º from the x plane
and a force of 3.0N acting at 0º from the x plane

Work out the resultant force and the angle

Answer 14

(image in notes)

Total force in x direction: 3.0 + 5.0cos60 = 5.5N
Total force in y direction: 5.0sin60 = 4.33N

Resultant force: √(4.33^2 + 5.5^2) = 7.0N

Direction: tanø = o/a = 4.33/5.5
ø = 38º