Question

A volcano shoots out blobs of molten lava, called lava bombs, from its summit. A geologist observing the eruption uses a stopwatch to time the flight of a particular lava bomb that is projected straight upward. If the time for it to rise and fall back to its launch height is 6 s, and its acceleration is 10 ms-2 downward, what is its initial speed?

Answer 1

Given:

The lava bomb is projected straight upward. The time taken to rise and fall back to its launch height is 6 s.

To find:

Initial velocity of projection?

Calculation:

Time for whole journey = 6 sec.

So, time for lava to reach max height is 6/2 = 3 seconds.

Now, we know :

• For constant acceleration (here a = -10 m/s²), we can use standard equation of Kinematics.

$\rm \: v = u + at$

$\rm \implies 0 = u - gt$

$\rm \implies u = gt$

$\rm \implies u = 10 \times 3$

$\rm \implies u = 30 \: m {s}^{ - 1}$

So, initial velocity of projection of lava is 30 m/s.