Velocity

• Physics

5.2 Velocity

Red slides are important do make sure you take notes!

Basic information

There are 4 kinds of velocity which we work with in year 2.

The velocity always has the symbol v in formula's.

Types of velocity

Truus is going to race on her bycicle against Jeroen.

When the starting signal sounds Truus accelerates from a standstill and cycles at a velocity of 8 km/h. Then she goes down a hill, as a result she accelerates to 12 km/h. When she goes over the finish line she has a velocity of 10 km/h. After the finish het smart watch says her overal speed was 9 km/h.

Types of velocity

Truus is going to race on her bycicle against Jeroen.

When the starting signal sounds Truus accelerates from a standstill and cycles at a velocity of 8 km/h. Then she goes down a hill, as a result she accelerates to 12 km/h. When she goes over the finish line she has a velocity of 10 km/h.  After the finish het smart watch says her overal speed was 9 km/h.

Vstart

Vfinal

V

V

Vavg

v	v start	v final	v avg
		. . . .

Speed at a certain time

Speed at the end

Speed at the beginning

The middle of the different speeds during a certain time

Types of velocity

v = the velocity at a certain time during a movement

vstart = the velocity at the beginning of the movement

vfinal = the velocity at the end of the movement

vavg = the average velocity of the whole movement.

Calculating vavg

vavg can be calculted with two formula's;

The first one can always be applied

v​avg​​​​​=​t​​s​​

v​avg​​​​​=​t​​s​​

Symbol	Name	Unit
v avg	Average velocity	m/s
s	Distance	m
t	time	s

v​avg​​​​​=​t​​s​​

Symbol	Name	Unit
v avg	Average velocity	km/h
s	Distance	km
t	time	h

vavg = s / t
The formula for s becomes;

1. s = vavg/ t
2. s = vavg x t
3. s = t / vavg
4. s= t x vavg

vavg = s / t
The formula for t becomes;

1. t = vavg/ s
2. t = vavg x s
3. t = s / vavg
4. t = s x vavg

Converting km/h to m/s

1 m / s =

Converting km/h to m/s

1 m / s =

1 m / 1 s =

Converting km/h to m/s

1 m / s =

1 m / 1 s =

0,001 km / 1 s =

Converting km/h to m/s

1 m / s =

1 m / 1 s =

0,001 km / 1 s =

0,001 / (1: 3600)h =

Converting km/h to m/s

So for m/s to km/h you multiply by 3,6

For km/h to m/s you divide by 3,6

v​avg​​=​2​​v​start+​​v​final​​​​

The second formula can only be used if you want to know the average speed of one type of movement (only an acceleration, decelaration or uniform motion)

Symbol	Name	Unit
v avg	Average velocity	m/s
v start	Velocity at the beginning of the movement	m/s
v final	Velocity at the end of the movement	m/s

v​avg​​=​2​​v​start+​​v​final​​​​

vavg = vstart + vfinal / 2
The formula for vstart becomes;

1. vstart = vavg / 2 - v final
2. vstart = vavg x 2 - v final
3. vstart = vavg / 2 + v final
4. vstart = vavg x 2 + v final

vavg = vstart + vfinal / 2
The formula for vfinal becomes;

1. vfinal= vavg / 2 - vstart
2. vfinal = vavg x 2 - vstart
3. vfinal= vavg / 2 + vstart
4. vfinal = vavg x 2 + vstart l

Which formula can you use to calculate the average speed of the whole movement shown in the graph?

1. vavg=​2​​(vstart+vfinal)​​
2. vavg=​t​​s​​
3. Both
4. None

Which formula can you use to calculate the average speed of the whole movement shown in the graph?

1. vavg=​2​​(vstart+vfinal)​​
2. vavg=​t​​s​​
3. Both
4. None

Which formula can you use to calculate the speed between t2 and t3?

1. vavg=​2​​(vstart+vfinal)​​
2. vavg=​t​​s​​
3. Both
4. None

Which formula can you use to calculate the speed between 0 and t2?

1. vavg=​2​​(vstart+vfinal)​​
2. vavg=​t​​s​​
3. Both
4. None

what is the velocity at t = 6 s?

What is vstart in A?

What is vfinal in A in km/h?

Calculate the average speed in part C of the graph

Calculate the travelled distance in part A of the graph