This document discusses speed, velocity, and examples involving distance, time, and calculations. It contains: 1) Definitions of speed as distance/time and velocity as displacement/time, with velocity being a vector and speed a scalar. 2) Examples of calculations for speed, distance, and time using the equations s=vt, t=s/v, and v=s/t. 3) A discussion of kinetic and potential energy, and examples using the equations for gravitational potential energy (Ep=mgh) and kinetic energy (Ek=1/2mv^2).

1. Dr Pusey

2. Recap: Speed and Velocity
Pretty much the same thing in Unit 2
𝑠𝑝𝑒𝑒𝑑 =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑖𝑚𝑒
(Scalar Quantity – e.g. 20m/s)
𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =
𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡
𝑡𝑖𝑚𝑒
(Vector Quantity – e.g. 20m/s East)

3. Other versions of the equation
𝑠𝑝𝑒𝑒𝑑 =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑖𝑚𝑒
𝑣 =
𝑠
𝑡𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =
𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡
𝑡𝑖𝑚𝑒
To get distance:
To get time:
To get speed:
𝑠 = 𝑣 × 𝑡
𝑡 =
𝑠
𝑣

4. Example Problems
 Dr Pusey runs 80 metres in 10 seconds, how fast can he
run?
 If the latest dipstick from Jackass gains a speed of 20m/s on
his skateboard, how far will he travel in 5 seconds?
 North Korea launches a rocket which reaches a speed of
100m/s towards the international space station which is
50,000m away, how long do the occupants have to escape?

5. Example Problems
 Dr Pusey runs 80 metres in 10 seconds, how fast can he
run?
 If the latest dipstick from Jackass gains a speed of 20m/s on
his skateboard, how far will he travel in 5 seconds?
 North Korea launches a rocket which reaches a speed of
100m/s towards the international space station which is
50,000m away, how long do the occupants have to escape?
𝑣 =
𝑠
𝑡
𝑠 = 𝑣 × 𝑡
𝑡 =
𝑠
𝑣

6. Example Problems
 Dr Pusey runs 80 metres in 10 seconds, how fast can he
run?
 If the latest fool from Jackass gains a speed of 20m/s on his
skateboard, how far will he travel in 5 seconds?
 North Korea launches a rocket which reaches a speed of
100m/s towards the international space station which is
50000m away, how long do the occupants have to escape?
𝑣 =
𝑠
𝑡
=
80
10
=8m/s
𝑠 = 𝑣 × 𝑡 = 20 × 5 = 100m
𝑡 =
𝑠
𝑣
=
50000
100
= 500 𝑠 = 8.3𝑚𝑖𝑛𝑢𝑡𝑒𝑠

7. Recap!
 Energy is the ability to make things happen
 Energy is the ability to do Work

8. Categories
 Potential Energy (stored energy)
 Gravitational Potential Energy (roller coaster, skiing)
 Chemical Potential Energy (food, batteries)
 Elastic Potential Energy (slingshot)
 Nuclear Potential Energy (Kaboooom!)
 Kinetic Energy (moving/active energy)
 Moving objects (trains, cars, you!)
 Moving particles (sound, heat)
 Moving waves (light)
 Moving electrons (electricity)

9. Gravitational Potential Energy
 A result of changes in an object’s height
𝐸 𝑝 = 𝑚𝑔∆ℎ
Potential Energy (J)
Mass (kg)
Height (m)
Acceleration due to
Gravity (9.8ms-2)

10. What Potential Energy does a 1 tonne wrecked car gain when a
crane lifts it off the ground and puts it on top of a 3 m high pile of
scrap?
Example

11. What potential energy does a 1 tonne wrecked car gain when a
crane lifts it off the ground and puts it on top of a 3 m high pile of
scrap?
Example Soln
𝐸 𝑝 = 𝑚𝑔∆ℎ
𝐸 𝑝 = 1000 9.8 3
𝑬 𝒑 = 𝟐𝟗𝟒𝟎𝟎 𝑱 𝒐𝒓
𝑬 𝒑 = 𝟐𝟗. 𝟒 𝒌𝑱
𝑚 = 1000 𝑘𝑔
∆ℎ = 3 𝑚
𝑔 = 9.8 𝑚𝑠−2
𝐸 𝑝 = ?

12. Kinetic Energy
 Kinetic energy = moving energy
 If an object is moving it has kinetic energy
Kinetic Energy (J)
Velocity (ms-1)
Mass (kg)
𝐸 𝑘 =
1
2
𝑚𝑣2

13. What is the Kinetic Energy of a 42 kg skateboard rider who has a
velocity of 3.7 m/s East?
Example

14. What is the Kinetic Energy of a 42 kg skateboard rider who has a
velocity of 3.7 m/s East?
Example Soln
𝐸 𝑘 =
1
2
𝑚𝑣2
𝐸 𝑘 =
1
2
42 3.72
𝐸 𝑘 = 287 𝐽
𝑚 = 42 𝑘𝑔
𝑣 = 3.7 𝑚𝑠2
𝐸 𝑘 = ?

15. Time for some Algebra
𝐸 𝐾 =
1
2
𝑚𝑣2
𝑚 = ?
𝑣 =?
𝐸 𝑃 = 𝑚𝑔ℎ
𝑚 =?
ℎ =?
𝑔 =?
On Your Data Sheet

16. Time for some Algebra
𝐸 𝐾 =
1
2
𝑚𝑣2
𝑚 =
2𝐸 𝐾
𝑣2
𝑣 =
2𝐸 𝐾
𝑚
𝐸 𝑃 = 𝑚𝑔ℎ
𝑚 =
𝐸 𝑃
𝑔ℎ
ℎ =
𝐸 𝑃
𝑚𝑔
𝑔 =
𝐸 𝑃
𝑚ℎ
On Your Data Sheet
Not On Your Data Sheet

17. Example
 Brodie is eating in class again. He eats a single Doritos potato chip, which
has a total energy of 40kJ. Dr Pusey chases him, and Brodie converts all of
the energy in the single Doritos chip to climb up a ladder to try and escape.
How far up does Brodie get? Assume Brodie has a mass of 40kg.

18. Example
 Brodie is eating in class again. He eats a single Doritos potato chip, which
has a total energy of 40kJ. Dr Pusey chases him, and Brodie converts all of
the energy in the single Doritos chip to climb up a ladder to try and escape.
How far up does Brodie get? Assume Brodie has a mass of 40kg.
ℎ =
𝐸 𝑃
𝑚𝑔
=
40000
40 × 9.8
= 102𝑚

19. Example
 Brodie loses his balance on the ladder and falls  Lucky for Brodie, the
swimming pool is right underneath him! Woohoo!
 At what speed does Brodie hit the pool?

20. Example
 Brodie loses his balance on the ladder and falls  Lucky for Brodie, the
swimming pool is right underneath him! Woohoo!
 At what speed does Brodie hit the pool?
𝑣 =
2𝐸 𝐾
𝑚
=
2 × 40000
40
= 2000 = 44.7𝑚𝑠−1
 We can also use this equation from last Semester  𝑣2 = 𝑢2 + 2𝑎𝑠
𝑣2
= 𝑢2
+ 2𝑎𝑠 = 0 + 2 × 9.8 × 102 = 2000, so 𝐯 = 𝟒𝟒. 𝟕𝐦𝐬−𝟏
WHOHHH!