Page 24 - 4167

3. Average acceleration over any period of time t is the change in

velocity v divided by a corresponding change in time

m m
 76  40
 v s s m
a    36
 t 3s  2s s 2

4. Instantaneous acceleration is the first derivative of speed with

respect to time, therefore
dv
a   2 B  6 Ct .
dt
Then
m m m
a  2 3   6 2   2s  30 ,
1
s 2 s 3 s 2

m m m
a  2 3  2  6 2  3  3s  42 2 .
2
s s s
2.From the height h=10m in horizontal direction a body is thrown

with a speed v  20 m s .
x
There're three levels of complication in it

1.The first level
To define :
- time t of motion,

- range S of flight of body,
- speed v of body at the moment
of falling
- direction of velocity at the

moment of falling (angle between
velocity and horizon)
To consider a body as a material

point and to neglect the resistance
of air.
In this case a body takes part in two
Figure 1.12 independent motions (fig.1.12 ):

free falling from the height h

23