Please need help to understand this

Question

A competitive skate board jumper comes off the ramp according to the function:

r(t) = −4.3t² + 20t, where t measures seconds after he jumps.

1. If the ramp he jumps off is 6 metres above the ground, modify the above function to represent the skateboard jumper’s height above the ground (h), t seconds after he jumps.
2. Given the function derived in part (1) above, determine the maximum height above the ground reached by the skateboard jumper. When does he achieve maximum height?
3. Determine the ski jumper’s velocity 3 seconds after he jumps.
4. How long does it take for the skateboard jumper to land (on the ground)?

Answer 1

1) r(t)=-4.3t^2+20t+6

2) Vertex is (m,n) m=-b/2a =-20/2(-4.3)=2.3 so t=2.3 second.The skateboard reaches its maximum height in 2.3 seconds.The maximum height is r(2.3)=-4.3(2.3)^2+20(2.3)+6=29.3 m

3) r(3)=-4.3(3)^2+20.(3)+6=27.3m

4)r(t)=-4.3t^2+20t+6 on the ground r(t)=0 so we have to solve the equation -4.3t^2+20t+6=0

t=4.93 after 4s and 93/100 the skateboard is on ground .