CHAPTER 3 STARTING, STOPPING AND MOVING
Name:
QUESTIONS
3.1 Distance and displacement
1.
What is the distance covered by an ant that travels 10 cm north and then 20 cm south?
2.
(a)
What is the displacement of a Volkswagen that travels west along a road for 10 km
and then south for 8 km?
(b)
What is the distance covered by the Volkswagen?
3.
If you were to walk 400 m to the east, in what direction and how far would you need to
walk in order to have an overall displacement of zero?
3.2 Speed and velocity
4.
5.
6.
Bill rides his bicycle 14 km east and then 17 km north over 2 h. What is his:
(a)
average speed?
(b)
average velocity?
An ant moving east along a desk travels 30 cm in 1.5 s. What is the ant’s:
(a)
average speed?
(b)
average velocity?
On the way to work, Jenni drives 1 km to the local shop taking 1 min to do so. She takes
5 min to decide what she wants, buy it and then get in the car again. Hitting peak hour
traffic, it takes her 30 min to travel the next 6 km to her workplace. What are
(a)
the total distance covered in the journey and
(b)
the average speed for the journey in km h–1?
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(c)
Is there any time that we can know her car’s instantaneous speed during the trip? If
so, when?
3.3 Acceleration
7.
A car, travelling north at 15 m s–1, uniformly increases its velocity to 24 m s–1 over 2.7 s.
What is the vehicle’s acceleration?
8.
A truck decelerates uniformly from 22 m s–1 at a rate of 4 m s–2 coming to rest at a set of
traffic lights. How long did the deceleration take?
9.
What will be the final velocity of a Nissan Pulsar that accelerates from rest at 5 m s–2 east
for 3.9 s?
3.4 Straight line motion
10. A semitrailer accelerates from 10 m s–1 to 30 m s–1 in 10 s as it travels down a straight
section of highway. What is the truck’s displacement during this time interval?
11. A cyclist, originally travelling at 20 m s–1, decelerates over a distance of 240 m until he is
travelling at 3 m s–1. Calculate the cyclist’s average acceleration.
12. A sprinter leaving the blocks in a 100 m race accelerates from rest to 4 m s–1 in the first
metre that she travels.
(a)
What is her acceleration over this distance?
(b)
How long does this acceleration take?
Review questions
Understanding
1.
Explain how it is possible for an object to be accelerating even though it is travelling at a
constant speed. Give an example.
2.
Under what conditions will an object’s speed and velocity have the same magnitude?
3.
What is measured by the speedometer of a car?
Application
4.
A car negotiating a series of city streets travels 200 m east, 400 m north and then 300 m
east again. What are the
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(a)
distance travelled by the car and
(b)
displacement of the car from its origin?
5.
What will be the displacement of a truck that travels a route that takes it 4 km north, then
6 km heading 30° west of north and then 2 km south?
6.
Calculate the speed of the following in m s–1:
(a)
a car that travels 100 km in 1.5 h
(b)
a bicycle that takes 2 min to travel 1 km
(c)
a sprinter who runs 100 m in 11.5 s
(d)
a truck that takes 4 min to travel 200 m in peak hour traffic.
7.
Calculate the speed and velocity of a plane that flies 800 km north and then 570 km east
over a 2 h time interval.
8.
What is the acceleration of a car that changes its speed from 20 m s–1 to 28 m s–1 in 3.0 s?
9.
A truck decelerates at a rate of 3.0 m s–2. What will be its speed after 5.0 s if it was
initially travelling at 80 km h–1?
10. A car travels around a slight bend in the road in 2.3 s. If it was originally travelling at
15 m s–1 north and was then travelling at 10 m s–1 at 20° east of north at the end of the
time interval, what was the car’s average acceleration?
11. A skateboarder travelling at 5 m s–1 comes to a hill down which he accelerates at a rate of
1.6 m s–2. If it takes him 4.3 s to reach the bottom of the hill, calculate:
(a)
the length of the hill
(b)
his speed at the bottom of the hill
(c)
the distance he has travelled down the hill by the end of the third second
(d)
the distance that he travelled in the fourth second.
12. What speed will a cyclist be travelling at after 8.0 s if he accelerates uniformly from rest
at a rate of 2.2 m s–2?
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QUEENSLAND PHYSICS
13. What is the acceleration of a car that is initially at rest but then travels 200 m in 10.0 s?
14. An aircraft flying due north at 980 km h–1 is subjected to high-altitude wind blowing
towards it at 88 km h–1 from 30° east of north. What will be the resulting velocity of the
aircraft?
15. On 6 May 1954, Roger Bannister became the first man to run one mile in under 4 min,
recording a time of 3 min 59.4 s. If 1 mile is equivalent to 1.609 km, what was
Bannister’s average speed in m s–1?
16. Make the following conversions:
(a)
20 km h–1 into m s–1
(b)
100 km h–1 into m s–1
(c)
15 m s–1 into km h–1
(d)
3 km s–1 into km h–1.
17. Sketch a velocity–time graph for the following:
(a)
a cyclist moving at a constant speed of 4 m s–1 for 5 s
(b)
a truck travelling at 12 m s–1 decelerating to rest at –1 m s–2
(c)
a man walking 50 m at 4 m s–1 then stopping suddenly and remaining stationary
for 3 s.
18. The displacement–time graph below represents the journey of a bus over a 60 min period.
(a)
At what times was the bus stationary?
(b)
What are the most likely reasons for the bus stopping?
(c)
What was the bus’s instantaneous speed at t = 30 min?
(d)
Determine the average velocity of the bus over the first 20 min of its motion.
(e)
Draw a velocity–time graph for the bus’s journey.
19. How far does a car travel if it accelerates from rest at 2.4 m s–2 for 12.0 s?
20. The displacement–time graph below shows the progress of two runners in a 400 m race.
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(a)
Who is the faster runner?
(b)
Who won the race?
(c)
What happened at point X?
(d)
Was this a fair race? Explain.
21. The velocity–time graph below shows the motion of cars A and B travelling along a
highway.
(a)
What is the speed of car A after 5 s?
(b)
How far does car B travel in 8 s?
(c)
What is car B’s acceleration at the 4 s mark?
(d)
Does car B catch up to car A? If so, when?
22. A motorcyclist accelerates uniformly from 10 m s–1 to 22 m s–1 over a distance of 300 m.
What was her acceleration?
Challenges
23. Two students were running a race over 400 m. Tony accelerates steadily at 1 m s–2 for
3.2 s and then keeps running at a constant speed for the rest of the race. Brett starts at the
same time, but then he trips over his shoelaces. If it takes him 4.0 s to tie his shoelaces and
he then accelerates at 1.8 m s–2 for 2.8 s before maintaining the same pace, does he have
any chance of winning the race?
24. A car cruises past a house at 15 m s–1; a dog sitting outside the house decides to chase the
car 1.2 s after it has passed. If the dog maintains an acceleration of 1.7 m s–2, how long
will the dog take to catch the car?
25. A police officer using a VASCAR marks out two points on the road, 100 m apart. If the
speed limit for the road is 60 km h–1, what is the minimum time that a car can take to
travel between the two points without exceeding the speed limit?
26. A truck activates the first sensor cable of an amphometer 0.5 s before activating the
second, which is 10 m away. If the speed limit in the area is 50 km h–1, could the driver
be pulled over for speeding?
27. A car entering a 50 m VASCAR zone at 20 m s–1 travels for 10 m before noticing the
police car hidden at the other end. If it then takes 0.7 s for the driver to start braking, what
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will his minimum deceleration need to be to reach the end of the zone with an average
speed of 60 km h–1 for the zone, and so avoid a ticket?
28. A car travels for 4 km of its journey at an average speed of 70 km h–1. What would the
car’s average speed for the next 4 km need to be if it is to have an overall average speed
of 50 km h–1 for the entire 8 km trip?
Notes:
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