Wednesday, 19 April 2017
Speed: Every Minute Counts...
Enter your individual response in the comment. Remember to label the parts as given.
(1) Describe clearly how would you approach the question?
(2) What is your final answer (round off to 3 SF if it is non-exact)
Duration: 5 minutes
Suggested Train of Thought...
The following suggestion reduces the 'redundant' working (updated on 23 April 2017)
Step 1: Draw out the info available
Speed of Wolf: 65 km/h
Little Red Riding Hood (LRRH) - start 35 minutes later; catch up after 130 km.
Step 2: Make inference
Since distance travelled by both Wolf and LRRH is the same,
then Wolf would have travelled 130 km.
By finding the time taken by Wolf, we can find the time taken by LRRH to travel the same distance (since she started 35 min later).
With this time, we can find the speed that LRRH travels at.
Step 3: Find time taken by Wolf. This will enable us to find amount of time LRRH has taken.
Distance by wolf = 130 km.
and time taken by Wolf = distance ÷ speed = 130 / 65 = 2 hours
Step 4: Find time taken by LRRH
Remember both Wolf and LRRH travel the same distance,
and LRRH started 35 min later than
Since wolf takes 2 hours to cover a distance of 130 km,
Time taken by LRRH = 2 h - 35 min = 85 min
Convert the time to h, we have 1 5/12 h
Step 5: Find speed that LRRH travels at
Speed = Distance ÷ Time
Speed = 130 km ÷ 1 5/12 h = 91.8 km/h (3 significant figures)