Question

How fast (metric units) is a ball going after 3.0 seconds if you drop it off a very high building? It would be 9.8 m/s^2 since gravity is a constant speed, right?

Answer 1

v=v0-gt
v0 = 0
v = -gt
v = -9.8 * 3 = -29.4 m/s
(minus because i assume positive y axis is up)

Answer 2

acceleration 9.8 m/s^2 means that every second you get 9.8 in velocity

Answer 3

Wait... so what is the answer to this problem?
A kid drops a rock in a dark well. After 3.0 seconds, he hears a splash. How deep in meters is the well?
Would that one be 29.4 also?

Answer 4

no

y = wellHeight -gt^2 / 2
0 = wellHeight - 9.8 * (3)^2 / 2
wellHeight = 44.1

Answer 5

44.1 meters

Answer 6

Do know the kinematic equations or Galileo's equation for a freely falling body?

Answer 7

No

Answer 8

You've never taken a physics course?

Answer 9

Do you know calculus?

Answer 10

I'm taking a physics course right now.

Answer 11

I'm in precal

Answer 12

Have you learned derivatives?

Answer 13

No

Answer 14

Sorry, I just returned. OK so if you haven't learned derivatives, then try the following and tell me if you get the answer. In fact post your solution please so if you've made any careless errors, I can check.

final speed = initial speed + acceleration x time

I'll be anticipating your response.

Answer 15

29.4 m/sec = 0 + 9.8 m/sec^2 * 3 sec

Answer 16

final speed = initial speed + acceleration x time

final speed = 0 m/s + (-9.8 m/s²)(3.0 s)

final speed = -29.4 m/s

∴ the ball is falling at a rate of 29.4 m/s.


Note: In the therefore statement the negative sign is omitted because I said that ... the ball is falling ... "Falling" implies descent which implies a negative direction. However, when substituting into the equation, it is necessary to replace the acceleration with -9.8 m/s², because gravity is a force that acts downward.


Do you understand now?

Answer 17

Yes

Answer 18

Are my answers not good enough to deserve a medal?

Answer 19

Haha fine...