Question

A boy throws a ball to the ground with force from a height of 10 m. After hitting the ground for the first time, it rises to a height of 20 m. Thereafter it rises only upto half the prior height on hitting the ground. What is the total distance travelled by the ball till it comes to rest?

• A. 80 m
• B. 40 m
• C. 50 m
• D. 90 m

Answer 1

The correct option is D 90 m

Distance travelled by the ball ground till it rises 20 m and then comes back to the ground = 40 m
Next it rises 10 m
Distance from ground to top to ground = 20 m, this continues
So we get the series as = 40 + 20 + 10 + . . .
The above series is in GP.
$\therefore$ Sum $=\frac{40}{1-\frac{1}{2}}=80m$
But the ball was first thrown form a height of 10 m.
Total distance = 80 + 10 = 90 m