Saturday 2 May 2015

Speed (Convergence + Difference in Distance)

Ali and Charles are both cycling to visit Bob.
They started from their houses at the same time and arrived at Bob's house at the same time.
The barber shop is located exactly halfway between Ali's and Charles' houses.
It is 140m from Bob's house.
Charles cycled at a speed 14m/min slower than Ali.
a) How much further did Ali cycle than Charles?
b) If Ali and Charles set off at 2pm, at what time did they arrive at Bob's house?

a) Difference in Distance = 140m × 2 = 280m
b) Shared Time = 280m ÷ 14m/min = 20min
End Time = 14 00 + 20min = 14 20 = 2.30pm
Concepts:
1) Difference in Distance (Convergence) = 2 x Distance of Meeting Point from Centre
2) Shared Time = Difference in Distance ÷ Difference in Speed
3) End Time = Start Time + Time Taken

Dan and Ellen started jogging at the same time along the same route.
Both did not change their speeds throughout.
After 35min, Dan was at the halfway point and Ellen was 300m behind.
Dan reached the end point 5 min before Ellen. What was the distance of the route?

300m × 2 = 600m
Ellen's Speed = 600m ÷ 5min = 120m/min
Halfway Distance = 120m/min × 35min + 300m = 4500m
Total Distance = 9000m

David and his brother John decided to cycle from his home to the library using the same route.
They started cycling at the same time. David cycled at a speed of 15km/h.
Both did not change their speed throughout the race.
When John covered 1/3 the distance, David was 4.5km ahead of him.
David reached the library at 4.45pm.
What time did John reach the library?

4.5km × 3 = 13.5km
13.5km ÷ 15km/h = 0.9h
= 0.9 × 60min = 54min
4.45pm + 54min = 5.39pm

A bakery and a library are 120 m apart. They are located between Hong's house and Jeya's house. The bakery is exactly half-way in between the two houses while the library is closer to Jeya's house. One day, Hong and Jeya started cycling from their houses at the same time and they arrived at the library together. Jeya cycled at 70 m/min while Hong cycled at a speed of 15 m/min faster than Jeya.
a) how much further did Hong cycle than Jeya?
b) how far is Jeya's house than the library?

Alex and Jack took part in a cycling race.
Jack cycled at a speed of 24km/h.
Both of them did not change their speed throughout the race.
When Alex reached the halfway point, Jack was 3km ahead of him.
Alex reached the end point at 12.10pm.
At what time did Jack reach the end point?
3km × 2 = 6km
6km ÷ 24km/h = 1/4 h = 1/4 × 60min = 15 min
12 10 - 15 = 11 55 = 11.55am







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