Question

Sam dropped a stoned from top of a cliff into the lake below. The stone travelled in the air with an average speed of 15 km/h and in the water with an average speed 3 km/h before hitting the bottom of the lake. The total distance from the top of the cliff to the seabed is 120 meters, and the stone's entire fall took 12 seconds. How long did the stone fall in the air and how long did it fall in the water?

• A. 7 seconds
• B. 5 seconds
• C. 6 seconds
• D. 7.5 seconds

Answer 1

The correct option is A 7 seconds

Distance travelled in air = 15x

Distance travelled in water = 3 (12 - x)

Total distance = 120 = 15x + 3(12-x) = 36 + 12x

$\Rightarrow$ x = 7 Seconds