Question

a rocket is fired straight up in the air at 160m/s. How long has it been in the air when its velocity is 23 m/s downward?

Answer 1

A rocket is fired straight up in the air at 160m/s. How long has it been in the air when its velocity is 23 m/s downward?

Solution

The velocity of the rocket (upward is positive direction):

$$v = v _ {0} - g t,$$

where $v_{0}$ - initial velocity, $g$ - an acceleration of gravity.

So we have

$$t = \frac {v - v _ {0}}{g}$$ $$t = \frac {160 - (-23)}{9.8} = \frac {160 + 23}{9.8} = 18.7 \, \text{s}.$$

Answer: 18.7 s.