Activities – Page 307 Answers
Remember
1. Write the formula used to calculate average speed in symbols and state which
quantity each symbol represents.
v = d/t
or
d = vt
or
t = d/v
v = average speed
d = distance travelled
t = time taken
2. Explain the difference between speed and velocity. Use an example to support
your explanation.
Velocity is a measure of the rate of change in position, and determines the direction of
movement as well as the size. Speed is a measure of the rate in which the distance is
covered and you needn’t determine the direction of movement.
Using Data
3. Determine the average speed of each of the following
a. a racehorse that wins the 3200 m Melbourne Cup in a time of 3 min 20
s (in m/s)
v = d/t
v = 3200/200
v = 16
the average speed of the racehorse was 16 m/s
b. a kangaroo fleeing from a dingo, which bounds a distance of 2.5 km in
3 min (in m/s)
v = d/t
v = 2500/180
v = 13.9
the average speed of the kangaroo was 13.9 m/s
c. a dolphin that just manages to keep up with a speeding boat for a
distance of 2 km for a period of 3 min (km/h)
v = d/t
v = 2/.05
v = 40
the average speed of the dolphin was 40 km/h
d. a sea turtle that is able to maintain its maximum speed for 0.5 h. In that
time it can swim a distance of 16 km (km/h)
v = d/t
v = 16/0.5
v = 32
the average speed of the sea turtle was 32 km/h
e. An Olympic swimmer who completes a 1500 m training swim in 15
min (km/h)
v = d/t
v = 1.5/0.25
v=6
the average speed of Olympic swimmer is 6 km/h
f. A mosquito that flies a distance of 2 m in 4 s (cm/s)
v = d/t
v = 200/4
v = 50
the average speed of the mosquito is 50 cm/s
4. Use your answers to question 1 to suggest answers to the 3 questions posed at
the top of the opposite page.
a. Could a kangaroo win the Melbourne Cup?
Kangaroo: 12.5 m/s
Racehorse: 16 m/s
No, unfortunately the kangaroo could not win the Melbourne cup. As you can see, the
Kangaroo’s speed is less than a racehorse’s speed meaning that the Kangaroo couldn’t
go as fast as a racehorse, and therefore wouldn’t be able to win.
b. Who would win a race between a sea turtle, a dolphin and Kieren
Perkins?
Sea turtle
Dolphin
Olympic swimmer
: 32 km/h
: 40 km/h
: 6 km/h
From the statistics above and judging that the race was short distance, the dolphin
would win, followed by the sea turtle then by an Olympic swimmer. Although, the
dolphin could only just keep up with the speeding boat for a length of 2 km, whereas
the Sea turtle maintained the same speed for 16 km. So if it was a long distance race, I
would say the sea turtle would come first, followed by the dolphin, then by an
Olympic swimmer
5. How long would it take you to walk from Melbourne to Sydney, a distance of
900 km, if you walked an average speed of:
a. 5 km/h without stopping?
t = d/v
t = 900/5
t = 180
It would take you 180 hours (7 and a half days)
b. 5km/h for 10 h each day?
days = 180/10
days = 18
It would take you 432 hours (18 days )
c. 1.5 m/s without stopping?
t = d/v
t = 900000/1.5
t = 600000
It would take 600000 seconds (1000 minutes, 166.67 hours or almost 7
days)
6. How far can a snail crawl if it moves at an average aped of 8.0 cm/min for:
a. 3 min?
d = vt
d=8x3
d = 24
the snail crawled 24 cm
b. 3 h?
d = vt
d = 8 x 180
d = 1440
the snail crawled 1440 cm
7. A swimmer swims the 100 m breast stroke event in 68 s. The event is
completed in a pool that is 50 m long. She finishes the event at the same end
of the pool from which she started. If she begins the event by swimming due
north, and takes 35 s to swim the first 50 m, calculate her:
a. average speed for the whole event
v = d/t
v = 100/68
v = 1.47
the average speed swimmer travels is 1.47 m/s
b. average velocity for the first 50 m
velocity = change in position/time taken
velocity = 50/35
velocity = 1.43
the average velocity Susie travels is 1.43 m/s North
c. average velocity for the whole event
velocity = change in position/time taken
As the position has not changed (he is back to where he started), the velocity over the
whole event is zero.
8. A swimmer completes a 1500 m race in 870 s. Calculate the swimmers
average speed in;
a. m/s
v = d/t
v = 1500/870
v = 1.72
average speed is 1.72 m/s
b. km/h
v = d/t
v = 1.5/0.24
v = 6.21
average speed is 6.21 km/h