# CAT Practice : Speed Time, Races

A car trying to overtake a truck travelling the same direction should travel at some extra speed!! And that is equal to ---

## Relative Speed

Q.12: A car of length 4m wants to overtake a trailer truck of length 20m travelling at 36km/hr within 10 seconds. At what speed should the car travel?
1. 12 m/s
2. 14.8 m/s
3. 12.4 m/s
4. 7.6 m/s

Choice C. 12.4 m/s

## Detailed Solution

Given :
car of length = 4 m
length of truck = 20 m
Speed of truck = 36 km/hr

Approach:
Total distance to be covered by the car 'd' = 20 + 4 = 24 m
Let speed of car be S1 m/s
Speed of truck S2 = 36 km/hr = 10 m/s
Both the car and the truck are travelling in the same direction and we know that to overtake the truck, the speed of the ca should be more than that of the truck.
Hence, relative speed = |S1 - S2|
Time to overtake = 10s

S = $\frac{d}{t}$

|S1 - 10| = $\frac{24}{10}$

S1 - 10 = 2.4
S1 = 10 + 2.4 = 12.4 m/s

Correct Answer: 12.4 m/s

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## More questions from Speed Time, Races

"Life is a race ... if you don't run fast ... you will be like a broken undaa" - Veerusahasra Buddhi