# Physics and algabra

1. Apr 15, 2004

### Joseph

What is the answer to how fast a ball fall's form 25 feet useing the formula d = 16t2

2. Apr 15, 2004

### outandbeyond2004

$$d = 16t^2$$

I assume that this gives the distance in feet. So,

$$t = \sqrt{25/16}$$

However you want the velocity of the ball at t = that number above. Can you finish now?

3. Apr 15, 2004

### Joseph

physics and algebra

I think the answer is 1 1/4 or 5/4 can you tell me if i am on the right track.?

4. Apr 16, 2004

### HallsofIvy

Staff Emeritus
Yes, that is correct.

5. Apr 16, 2004

### outandbeyond2004

This is only the time, not the velocity at that time. You still need to find velocity as a function of time. Can you do that?

6. Apr 17, 2004

### FUNKER

if you find the first derivative of distance as a function of time this wud give you a formula for velocity if acceleration is not constant, in this case it wud be
d'(t) = 36t.

7. Apr 17, 2004

### The_Brain

Judging by the title, I don't think Joseph would know calculus. However, I could be wrong.

8. Apr 17, 2004

### DrMatrix

Eh. . . The acceleration is constant. your post should read: "If you find the first derivative of distance as a function of time this would give you a formula for velocity, in this case it would be d'(t) = 36t."

9. Apr 17, 2004

### jdavel

Froget calculus; judging by this, "d'(t) = 36t" and the number of times it's been quoted in the last few posts, I don't think anyone here knows what 2*16 is!

10. Apr 18, 2004

### rj

hey,
d = u*t + 1/2 a*t2
=> 25 = 1/2 g*t2 ....................(1)
but according to the question
d = 16 t2
or
25 = 16t2.................................(2)

comparing (1) and (2)
1/2g=16

g= 32 feet/ second squared ??

or 12.8 metres/second squared ??

was the ball really undergoing a free fall ??