An egg falls from rest atop a 15-m tall tree. Show that it takes 1.7s for it to hit the ground below.

Answer 1

Daisha,
I can help you with this problem, but not with all of them. They are all pretty standard problems in a high school physics subject. Any high school physics text will give you lots of worked out examples.
Here:
One way to do it:
acceleration = -9.8 m/s^2 (gravity down)
velocity v = intial velocity + a t
so
v = 0 - 9.8 t
height = initial height + Vi t + (1/2) a t^2
so
0 = 15 + 0 t - (1/2)(9.8) t^2
so
4.9 t^2 = 15
t^2 = 3.06
t = 1.74 seconds

another way to do it:
Potential energy at 15 meters compared to on ground = m (9.8)(15) = 147 m Joules
that will be the kinetic energy at ground
(1/2) m v^2 = 147 m Joules
v^2 = 294
v = 17.15 m/s at ground
so average speed down = 17.15/2 = 8.57 m/s
15 = 8.57 t
t = 1.74 seconds again

Answer 2

thank you for your help. If we can't use joules and I don't know anything about the height. in this question is height and distance the same?

Answer 3

Yes, the distance it fell is the height, 15 meters.