A car is travelling at a speed of 90 km/h. Brakes are applied so as to produce a uniform acceleration of -0.5 m/s2(metre per sec. Square). Find how far the car will go before it is brought to rest?

The only thing that mkes this question inconvenient is that it uses a mixture of units ... speed in km/hr, and acceleration in m/s².  You can't directly mash those together.

What's the speed when we express it in m/s ?

Speed = (90 km/hr) · (1,000 m/km) · (1 hr/3,600 sec)

Speed = (90 · 1,000 · 1 / 3,600) · (km-m-hr / hr-km-sec)

Speed = 25 m/s

OK great !  

-- The car is traveling at 25 m/s when the brakes are applied.

-- The brakes slow it down by 0.5 m/s every second.

-- So it takes (25/0.5) = 50 seconds to stop the car.

-- During that time, the car's average speed is (1/2)·(25m/s + 0) = 12.5 m/s .

-- Moving at an average speed of 12.5 m/s for 50 sec, the car travels

(12.5 m/s) · (50 s)  =  625 meters

powerful computers now, not then