Upload
danielle-schmitt
View
219
Download
2
Tags:
Embed Size (px)
Citation preview
Linear Accelerated MotionPart 1
For the Higher Level Leaving Cert Course
©Edward Williamson, Applied Maths Local Facilitator, Coachford College, Co Cork
www.pdst.ie
Ordinary LevelBefore you start this course, it is highly recommended you complete the basics in the ordinary level course.This will give you the basics in the different sections
www.pdst.ie
Types of Questions
Velocity Time GraphPeriod of Constant SpeedNo Period of Constant Speed
Gravity/Vertical Motion2 Bodies in Motion/OvertakingPassing successive Points/2 points
www.pdst.ie
www.pdst.ie
Velocity Time GraphArea under Curve = distance travelledSlope (y over x) is accelerationUse equations of motion for constant
acceleration period only.
a
d
t
t
2
1avelo
city
time
d
t1 t2
www.pdst.ie
Example 1.1 [LC:1997 Q1(a)]
A particle, moving in a straight line, accelerates uniformly from rest to a speed v m/s. It continues at this constant speed for a time and then decelerates uniformly to rest, the magnitude of the deceleration being twice that of the acceleration. The distance travelled while acceleration is 6 m. The total distance travelled is 30 m and the total time taken is 6 s.
Draw a speed time graph and hence or otherwise, find the value of v.
Calculate the distance travelled at v m/s
www.pdst.ie
Vel
ocity
Time2t t
v
6-3t
Area = 6
Area of whole shape is 30
Area of acceleration = 6
6
6)2(2
1
tv
vt
Relate Times together
www.pdst.ie
Total Area = 30 m
smv
v
tv
tvtvv
tvvt
/5.6
30)6(2
1)6(366
)6(
302
1366
302
1)36(6
13
12
5.6
66
vt
sm
vtArea
/21
5.6))13
12(36(
)36(
Finding area of triangles and rectangle
Finding Distance (area of rectangle)
www.pdst.ie
Example 1.2 [LC: 1994 Q1(a)]
A lift in a continuous descent, had uniform acceleration of 0.6 m/s2 for the first part of its descent and a retardation of 0.8 m/s2 for the remainder. The time, from rest to rest was 14 seconds.
Draw a velocity time graph and hence, or otherwise, find the distance descended.
www.pdst.ie
Vel
ocity
Timet 14-t
0.60.8
Fact: Ratio of accelerations
83
4
6.0
8.0
14
tt
t
Ratios are easier as fractions
www.pdst.ie
sm
tv
atuv
/8.4)8(6.0
6.0
m
Area
6.33
)8.4)(6(2
1)8.4)(8(
2
1
When Accelerating
Total Distance = Total Area
Area of left triangle and area of right
triangle
www.pdst.ie
Example 1.3 [LC: 2006 Q1(a)]
A lift starts from rest. For the first part of its descent, it travels with uniform acceleration f. It then travels with uniform retardation 3f and comes to rest. The total distance travelled is d and the total time taken is t.
i. Draw a speed time graph for the motionii. Find d in terms of f and t.
www.pdst.ie
33
2
1 f
f
t
t
4
3t
4
t
4
343
ftv
ftv
f3f
Vel
ocity
Timet1
t2
Ratios of Times
Total Area
Told t in the question is total time
Use info on acceleration
www.pdst.ie
8
3)
4
3(22
))(4(2
1))(
4
3(2
1
2ftfttvt
vt
vt
Area
Area of left
Triangle
Area of right triangle
www.pdst.ie
Now try some questions by yourself on the attached sheet
www.pdst.ie
Section 2Passing a number of
points
www.pdst.ie
Passing number of points
Always start from same point to use same initial velocity
i.e. if question is a to b, b to c and c to d; you treat it as
a to ba to ca to d
www.pdst.ie
Example 2.1 [LC:2003]
The points p, q, and r all lie in a straight line.A train passes point p with speed u m/s. The
train is travelling with uniform retardation f m/s2.The train takes 10 seconds to travel from p to q and 15 seconds to travel from q to r, where |pq|=|qr|=125 metres.
i) Show that f=1/3ii) The train comes to rest s metres after
passing r. Find s, giving your answer correct to the nearest metre.
www.pdst.ie
125 m 125 m
p q r
u = ua = -f
p to q
2
2
1atuts
fu
fu
5010125
)10(2
110125 2
fu
fu
2
62525250
)25(2
125250 2
p to rStart from same point
each time i.e. p
w
s
www.pdst.ie
17.14;3
1 uf
ms
mx
xu
fxu
51250301
301
)3
1(20
20
2
22
Solving
p to w
Get total distance from p to w and
then subtract distance p to r
from it
www.pdst.ie
Example 2.2 [LC:1988 Q1 (a)]
A particle moving in a straight line with uniform acceleration describes 23 m in the fifth second of its motion and 31 m in the seventh second. Calculate its initial velocity
www.pdst.ie
Fifth Second is between t=4 and t=5 Initial Velocity is u and acc=a
t=4, u=u, s=s, t=4, a=a
aus
aus
84
)4(2
1)4(
4
24
t=5, u=u, s=s, t=5, a=a
aus
aus
5.125
)5(2
1)5(
5
25
235.445 auss From Question
t=7, u=u, s=s, t=7, a=at=6, u=u, s=s, t=6, a=a
aus
aus
186
)6(2
1)6(
6
6
2
aus
aus
5.247
)7(2
1)7(
7
27
315.667 auss
smu /5
www.pdst.ie
Now try some questions by yourself on the attached sheet