- #1
TheRedDevil18
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Homework Statement
A ball is projected vertically upward with a velocity of 30m/s. It strikes the ground after 8's.
1.1) Determine the height of the building
1.2) Find the height of the ball relative to the ground as well as its velocity at t=3 and t=5
1.3) At what time will its velocity be 25m/s, downward?
Homework Equations
equations of motion
The Attempt at a Solution
1.1) Okay, I worked out the total time to go up and got 3's and then doubled it for coming down and got 6's (edge of the building). 8-6=2's coming down from top of the building.
delta y=vi*t+0.5*a*t^2
height of building = 79.6m
1.2) at t=3's, v=0
delta y = 45.9m
Relative to ground:
79.6+45.9=125.5m
at t=5's
vf = vi+at
= 0+(9.8)*5
= 49m/s - 30m/s
= 19m/s
delta y = 19.6m+79.6
= 99.2m relative to the ground
1.3) vf = vi+at
t = 2.55+3
= 5.55's
Could someone please check?