Two cars start at the same time from one point and move along two roads at right angles. Their speeds are 36 km/hr and 48 km/ hr respectively. After 15 seconds, what will be the distance between them?

There are two speeds given in the question, 

V₁ = 36km/hr 

V₂ = 48km/hr

converting them in m/s we have

V₁ = 36x1000/3600 = 10m/s

V₂ = 48x1000/3600 = 40/3 m/s

After 15 seconds, distance covered by both cars are,

distance =  speed x time 

D₁ = V₁ x 15 = 10 x 15 = 150m

D₂ = V₂ x 15 = (40/3) x 15 = 200m 

Also it is said that they are moving at right angles, 

hence D₁ & D₂  becomes the two sides of that triangle ,

and the hypotenuse will give the distance between the two cars 

let D be the distcance between the two cars

therefore by By Pythagoros Theorem,

D² = D₁² +  D₂²

D² = 150² + 200² = 22500 + 40000 = 62500

D = √62500 = 250m 

therefore the distance between the two cars after 15 sec is 250m