physics 2 part question?

Question

(Part 1)
A stone falls from rest from the top of a cliff.
A second stone is thrown downward from the
same height 2.4 s later with an initial speed of
47.04 m/s. They hit the ground at the same
time.
The acceleration of gravity is 9.8 m/s^2.
How long does it take the first stone to hit
the ground? Answer in units of s.

(Part 2)
How high is the cliff? Answer in units of m.

Answer 1

Part 1

s = ut + (at^2)/2

s is same for both stones
but second stone takes 2.4 s less than first
u (initial speed of second stone) = 47.04
u first stone = 0

therefore:
47.04 t + (9.8 t^2) / 2 = (9.8(t + 2.4)^2) / 2

Simplifying:

27.44 t = 19.6

t = 0.714 s

Time for first stone = 2.4 + 0.714
= 3.11 s

Part 2:

Height = s = (9.8 (3.11)^2)/2
= 47.524 m
= 47.5 m

Answer 2

Hans' initial equation looks okay. (t = the time in seconds for the SECOND (thrown) stone to get to the ground.)

I think the problem is in the simplifying of the eqtn. (That usually is grungy work.)
I get 1.2 seconds for t. The first stone of course takes 3.6
seconds. The cliff height becomes 63.5 meters.

Answer 3

ok, i think of i will help you with this undertaking. (nonetheless it relatively is basically the 2nd question i've got responded on yahoo). right this is a physics formulation I basically love. Vf^2=Vi^2+2A*D. in actuality, the suitable velocity squared equals the preliminary velocity squared + 2 circumstances acceleration circumstances distance. i might propose changing a million.6 cm to .0016 meters first. fixing for A, we've: Acceleration= (velocity very final^2 minus velocity preliminary^2)/(2*.0016) ^2 potential to sq.,btw. i'm going to permit you paintings that out your self. For area 2, you ought to use the formulation D=(a million/2) A*T^2 seem on the internet website I published under.

Answer 4

Part 2.
2nd stone
Ek = 0.5mv^2 = 0.5m(47.04^2)
Ep = mgh = m(9.8)h
Ep = Ek
9.8h = 1106.38
h = 112.89m; height of the cliff

Part 1
1st stone
Ep = Ek
mgh = 0.5mv2
m(9.8)(112.89) = 0.5mv^2
1106.32 = 0.5v^2
v = 23.52; velocity when hits the ground
Ek = vt^2 = 23.52t^2
t = 4.85 seconds.