Question

Physics help please!! Will give medal! A rock dropped from a high platform is moving at 24 m/s downward when it strikes the ground. Ignore air resistance. How fast was the rock moving when it had fallen only one-fourth of the distance to the ground?

18.0 m/s

12.0 m/s

8.0 m/s

6.0 m/s

Answer 1

@lonnie455rich

Answer 2

I'm thinking it's either 6 or 8

Answer 3

final velocity is 24 m/s and gravity is 9.8 m/s so what equations do you have for these two

Answer 4

v^2 = u^2 + 2ax is what my teacher told us to use I think

Answer 5

define your variables.

Answer 6

right sorry! x=displacement u= initial velocity v = final velocity t= time and a=acceleration which I suppose is 9.8m/s?

Answer 7

you know your initial velocity is 0 correct.

Answer 8

yes

Answer 9

now what do I do? @lonnie455rich

Answer 10

plug and chug to dind displacement

Answer 11

then plug that displacement in to find final velocity at 1/4 the displacement

Answer 12

ok...

Answer 13

24 = 0^2 + 2(9.8)(d)?

Answer 14

yes

Answer 15

no

Answer 16

ya. that is it. unless you are supposed to square the final velocity. i cant remember

Answer 17

i think you square it

Answer 18

yeah sorry I meant 24^2

Answer 19

yep

Answer 20

sorry i have to go but @petiteme can help. you should have it figured out, but just in case.

Answer 21

@petiteme

Answer 22

is it 29.4 approximately?

Answer 23

I mean 7.4?

Answer 24

@petiteme

Answer 25

Did you solve it?

Answer 26

yes 7.4 is what I got

Answer 27

@petiteme

Answer 28

hello????