Q#27 (Past Exam Paper – June 2016 Paper 11 Q8)
Two cars X and Y are positioned as shown at time t = 0.
They are travelling in the same direction.
X is 50 m behind Y and has a constant velocity of 30 m s-1. Y has a constant velocity of 20 m s-1.
What is the value of t when X is level with Y?
A 1.0 s B 1.7 s C 2.5 s D 5.0 s
Solution:
Answer: D.
Both cars X and Y are travelling at the constant speed. Since car X is travelling faster, it would, at one point, be level with car Y.
Let the time at which the cars are level be t.
Speed = Distance / time
Distance = Speed × Time
Distance travelled by car Y in this time t = 20t
Initially, car Y was 50 m in front of car X.
Position of car Y at this time t = 50 + 20t
The cars would be level at the same time (t).
Distance travelled by car X = 30t
When the cars at level, they would be at the same position.
Position of car X = Position of car Y
30t = 50 + 20t
10t = 50
Time t = 50 / 10 = 5.0 s
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