I may have an idea of what you can do next time to see the
cruising speed of a bus on an Expressway.
EXPERIMENT 1
Take 2 points on a map (A and B) on exits/entrances of a target
expressway.
Measure the distance, d of A and B through the bus route. (NOT
DISPLACEMENT!)
Record the value of d.
Take a bus.
When bus goes past Point A, start a stopwatch.
When bus goes past Point B, stop the stopwatch.
Record the value, t1.
Try the experiment with the same bus for a minimum of 2 tries (to
ensure accuracy by averaging results). Record these values t2 and
t3.
Find the mean time taken for the bus to cruise on this expressway
by:
(t1 + t2 + t3)/3. Record this as t.
Calculate the average speed of the bus by using the formula d/t.
Hence that is your approximate speed of the bus. (you have to
correct the distance to km or m, and the time to hour or seconds,
depending on whether you want S.I. units or speedometer
values)
DO NOT use values of t1, t2 or t3 that have been interrupted (for
e.g. bus has to apply emergency brakes, or traffic jam)
Word of precaution: Correct all values of d and t used to their
respective significant figures.
Or if you want a more interesting experiment...
Draw a table of 2 columns and 6 rows.
Label the first column d/km and the second column t/h
Pick Points A and B along an expressway. Measure the length, d1 of
the distance of Points A and B where the bus will use. Record d in
the table.
When the bus goes past Point A, start a stopwatch. When the bus
goes past Point B, stop it, record t in the same table.
Take 4 more readings of d along the same expressway with the same
bus and repeat the experiment. Take the readings of t that are
corresponding to the values of d you stated.
Plot a graph of t(h) against d(km). Draw a best fit line.
Find the gradient, S of the graph.
Find 1/S. This value is the average speed of the bus.