How fast is the balloon moving when it is halfway down the building (assume no friction)?

## Responses (1)

So the question is how fast when it drops 22 meters?

s = (1/2)at^2 where a is assumed to be 9.81 m/s^2

That poses a new question: How much time to fall 22 meters?

d = at

t = d/a = 22/9.81 =2.2426 s

s = 9.81/2 x 5.02929 = 24.6687 m/s

When assembling your equation you need to remember that the units have to cancel same as any other fraction.

s (meters/sec) = (1/2) x (9.81 m/sec^2) x (t sec)^2 That does not make sense because seconds cancel totally and there is no /sec in the answer. So I have misremembered the equation. (At my age that happens a lot.) Do it again:

s = (1/2) at = 9.81/2 x 2.2426 = 11 m/s Now the units come out right.

The answer choices are 20.78 m/s

39.81 m/s

19.68 m/s

26.92 m/s

Ya know, I work from memory and it's been 25 years since I did any of this work. It occurs to me now that s=(1/2)at is the AVERAGE speed. The final speed is twice that. So pick the answer closest to 22 meters per second, 20.78.

People often use values for a other than 9.81.

Thanks alot , so the answer is 11m/s?