Sunday 3 May 2015

Speed Concepts (Leaving Behind)

Unsorted

Mei and Lin were in a bicycle race. Mei was travelling at a constant speed of 20 km / h and hoth of them did not change their speed. When Lin completed half the race, Mei was 3.5km ahead. Mei completed the race at 10.45am. What time did Lin complete the race? 


Dan and Ellen started jogging at the same time along the same route shown below.
Both did not change their speeds throughout.
After 35 min, 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?


Sharon and Xinyi started cycling at the same time along a 4.5 km track.
Both did not change their speeds from start to finish.
Sharon cycled at 375 m/min.
When she reached the end of the track, Xinyi was 600 m behind her.
What was Xinyi's cycling speed in m/min?


Given: Total Distance, Difference in Time, Slow Speed
Answer: Fast Speed

Andy and Bryan set off on a 180 km journey. Andy completed the journey 30 minutes earlier than Bryan. If Bryan travelled at a speed of 72 km/h, find Andy`s speed.



Bryan's Time = 180 km / 72 km/h = 2 1/2 h
Andy's Time = 2 1/2 h - 1/2 = 2 h
Andy's Speed = 180 km / 2 h = 90 km/h


Given: Leave Behind Time, Leave Behind Speed, Distance Fragment
At 8.30 a.m., Mike and Jenny set off at the same time from X to Y. At 11 a.m., Mike had completed his journey but Jenny had covered over 5/8 of the journey. Jenny's speed was 54 km/h slower than Mike's.

a) Find the distance between X and Y
b) At what time would Jenny complete her journey?

Leave-Behind Time = 11 00 - 08 30 = 2 h 30 min = 2 1/2 h
Leave-Behind Distance (3/8 of Journey)  = 54 km/h x 2 1/2 h = 135 km
X to Y Distance =  360 km

Mike's Speed = 360km / 2 1/2h = 144 km/h
Jenny's Speed = 144 - 54 = 90 km/h

Jenny's Remaining Time = 135km / 90km/h = 1 1/2 h = 1 h 30 min
Jenny's End Time = 11 00 + 1h 30 min = 12 30 = 12.30 a.m.

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