If it takes 3 seconds for a rock to hit the ground, what was its speed before impact?

Question

That is, if objects on Earth accelerate at 9.8m/s^2. I don't understand this at all. Someone please help and thoroughly explain it to me, thanks. :)

... darn physics..

Answer 1

The velocity you are looking for is called "Final Velocity", and there are two fomulas to solve for it: the square root of (the initial velocity^2 + 2 x Acceleration x Distance) -- or (Time x Acceleration + Initial Velocity)

In you case, you want to use the second formula -
3 seconds X 9.8m/sec^2 + 0m/s (assuming the rock was dropped, and not thrown)

You're answer should be 29.4 m/s

I hope that helps :)

Answer 2

initial = 0m/s
1s = 9.8m/s
2s = 19.6m/s
3s = 29.4m/s

Explanation :
Acceleration = 9.8m/s^2
time = 3s
Velocity before impact = 9.8m/s^2 x 3s
= 29.4m/s

Gravitation is a phenomenon through which all objects attract each other. Modern physics describes gravitation using the general theory of relativity, but the much simpler Newton's law of universal gravitation provides an excellent approximation in many cases. Gravitation is the reason for the very existence of the Earth, the Sun, and every object in the universe; without it, matter would not have coalesced into masses and life would not exist. Gravitation is also responsible for keeping the Earth and the other planets in their orbits around the Sun; the Moon in its orbit around the Earth; the formation of tides; and various other natural phenomena that we observe. See Newton's cannonball.

Answer 3

Well if that's the complete question, you should first scold your physics teacher. Not enough information is given. Does this object have an initital velocity? Is it dropped or is it thrown up in the air?

We'll assume it's dropped from rest.

An acceleration of 9.8 m/s^2 means just this: for every second that passes, the speed of the object increases by 9.8 m/s. hence 9.8 m/s /s.

So in other words it's velocity when it hits the ground is 29.43 m/s.

Answer 4

I'm thinking that after 1 second it is going 9.8m/s, after two seconds it is twice that, and after 3 seconds it is 3 times that.

Answer 5

use this fomula
Vf = at + Vi

Vf = final velocity
a=accelertion
t= time
Vi = inital velocity

assume the block is released from rest.

Vf = (-9.8)(3) + 0
Vf = -29.4m/s

hope this helps