Question 5.5. Sandra throws an object into the air with an initial vertical velocity of 38 feet per second, from a platform that is 30 feet above the ground. How long will it take the object to hit the ground?
(Points : 1)
1 second
2 seconds
3 seconds
4 seconds
i think its 4 sec
Question 5.5. Sandra throws an object into the air with an initial vertical velocity of 38 feet per second, from a platform that is 30 feet above the ground. How long will it take the object to hit the ground?
(Points : 1)
1 second
2 seconds
3 seconds
4 seconds
6 answers
And why do you think it took 4 seconds?
(wrong guess by the way)
(wrong guess by the way)
in this system of units, remembered only by ancient mathematicians, g = 32 ft/s^2 approximately.
so
a = - 32
v = Vi - 32 t
= 38 - 32 t
h = Hi + Vi t + (1/2) a t^2
0 = 30 + 38 t - 16 t^2
or
16 t^2 - 38 t - 30 = 0
8 t^2 -19 t -15 = 0
solve that quadratic for t, use the positive result (obviously it was also at zero height before it started :)
so
a = - 32
v = Vi - 32 t
= 38 - 32 t
h = Hi + Vi t + (1/2) a t^2
0 = 30 + 38 t - 16 t^2
or
16 t^2 - 38 t - 30 = 0
8 t^2 -19 t -15 = 0
solve that quadratic for t, use the positive result (obviously it was also at zero height before it started :)
4 is not it I think
but 3 kind of looks reasonable
but 3 kind of looks reasonable
I think it's 3 too
Yea, I just took the quiz and 3s is the correct answer
1 answer