posted by Jacke on .
1.if a ball is thrown into the air with a velocity of 35ft/s, it's height in feet after t seconds is given by y=35t-10t^2. Find the averag velocity for the time period beginning when t=4 and lasting 0.05s.
2.if a ball is thrown into the air with a velocity of 30ft/s, it's height in feet after t seconds is given by y=30t-20t^2. Find the instantaneous velocity when t=3
Last time I was on this earth, gravity would cause an equation of the type
y = -16t^2 .....
So assuming you have a typo and it should have been
y = 35t - 16t^2
the ball would not be in the air for 4 seconds,
so your whole first question is actually just gibberish.
Once you fix it, find y when t = 4
find y when t = 4.05
evaluate: ( y(4.05) - y(4) )/.05
2. same thing here,
after 3 seconds the ball has reached the ground, and no longer has any velocity
if we ignore reality,
dy/dt = 30 - 40t
when t = 3
dy/dt = 30 - 120 = -90 ft/s
when t=4, y = 35(4) - 16(16) = -20
There is no error in the problem.
I see the typo as specifying feet. In metric units, g=9.8, or roughly 10, so Jacke, redo the calculations, with g=10 and get the correct answer.
Is it ok if I get a negative answer???
OK thanks I got it