helpppppppppppp please

the ball has a mass of 0.15kg and is dropped from an initial height of 1.2m. After impact the ball rebounds to a hight of 0.75m

Calculate the speed of the ball immediately BEFORE impact and AFTER impact???

Reply 1

dh00001

before impact. height times acceleration of gravity
after well depends how much after. i would say 0 because it has yet to bounce back up. not sure on that one really
its abit of a trick question

Reply 2

F1 fanatic

kevpang

you need to use the suvat equations I think, so initially:

s=1.2m u=0 v=? a=9.81m/s^2

use v^2=u^2+2as to get v

then on the way back up write it out again

s=0.75m u=? v=0 a=-9.81

note the minus because acceleration is now down and it's going up.

use the same equation as before and solve for u

Reply 3

kevpang

but u cant root the negative V square

Reply 4

kevpang

the ball has a mass of 0.15kg and is dropped from an initial height of 1.2m. After impact the ball rebounds to a hight of 0.75m

how to Calculate the momentum ????

Reply 5

F1 fanatic

kevpang

but u cant root the negative V square

it's not negative, or it shouldnt be. where is it negative?

Reply 6

F1 fanatic

kevpang

the ball has a mass of 0.15kg and is dropped from an initial height of 1.2m. After impact the ball rebounds to a hight of 0.75m

how to Calculate the momentum ????

you should keep this in the same thread as before.

However, momentum is by definition m*v which is all you need, given you worked out v in the previous part.

Reply 7

Desert Eagle

you could do this with energy. gpe gained = k.e. lost
therefore at the begining, it has gpe = (0.15x9.81x1.5) Joules
the loss in gpe = the gain in k.e.
therefore 0.5x0.15xv^2 = 0.15x9.81x1.5
This is the before velocity.

Then the ball gains 0.15x9.81x0.75 gpe, which means it has this much k.e. after it hits the ground, so the after velocity is
0.5x0.15xv^2 = 0.15x9.81x0.75

Reply 8

kevpang

no u cant, cos it is not a bloody elastic collision

Reply 9

Desert Eagle

i never said it was an elastic collision..... if you bothered to think for a sec and actually work out the before and after velocity i wrote, youd see that the velocity before is greater than the velocity after, so its not an elastic collision.