Question

Two motorboats, traveling at 5 and 10 km/h head directly towards each other. They begin at a distance of 20 km from each other. How far apart are they (in km) one minute before they collide?
1. 1/12
2. 1/6
3. 1/3
4. 1/8
5. 1/4

Answer 1

Correct Answer - Option 5 : 1/4

Given:

Speed of the two boats are 5 km/h and 10 km/h respectively and distance of separation between them is 20 km.

Concept:

This is a typical problem of relative speed. As the boats are moving towards each other, the speed of the stream cancels out.

Formula used: s = v × t

Where, s = distance of the journey, v = speed, t = time taken

Calculation:

Relative speed of the boats = (10+5) km/h = 15 km/hr

So, to calculate the separation between them just 1 minute before the collision, we have to calculate the relative distance traversed by them in 1 minute.

They travel 15 km in 60 minutes.

So, distance traversed in 1 minute = 15/60 = ¼ km

So, distance between them 1 minute before collision = ¼ km