Question 395288
An Olympic ski jumper skis off a spring board. Her height h, in metres, above
 the ground, t seconds after she jumps, is given by h(t)= -4.9t^2 + 20t +15.
 Algebraically determine the approximate instantaneous rate of change in her
 height at 2 seconds and describe what is happening at that time.
:
A good way to see what is happening is to graph this equation
{{{ graph( 300, 200, -4, 6, -10, 50, -4.9x^2+20x+15) }}}
:
It looks like it is at max height at 2 sec,
 prove that with the axis of symmetry formula x = -b/(2a), where a = -4.9, b=20
x = {{{(-20)/(2*-4.9)}}}
x = {{{(-20)/(-9.8)}}}
x = 2.04 sec it is at max height
:
At this point it is changing from an upward path to a downward path
There is no change in height at 2 sec