Expert: Paul Klarreich - 3/25/2008

Question
after a jump from  a plane the height (in metres) of a skydiver above the ground is given by H=1800-5t2, where t is the time (in seconds) after jumping.

a) how high was the palne at the moment the skydiver jumped?

b) what is the skydiver's height above the ground after 12 seconds?

c) what is the approximate time taken for the skydiver to reach  the ground.

d) How long does it take for the skydiver to reach a height of 900m above the ground? (Give your answer correct to one decimal place.)

Answer
Questioner:   jessie
Category:  Advanced Math
Private:  No
 
Subject:  quadratic problems
Question:  after a jump from  a plane the height (in metres) of a skydiver above the ground is given by H=1800-5t2, where t is the time (in seconds) after jumping.

a) how high was the palne at the moment the skydiver jumped?

b) what is the skydiver's height above the ground after 12 seconds?

c) what is the approximate time taken for the skydiver to reach  the ground.

d) How long does it take for the skydiver to reach a height of 900m above the ground? (Give your answer correct to one decimal place.)
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Hi, Jessie,
 
My instructions to questioners include:

(5) Tell me what you already did, and what you are studying --

Since you didn't, I conclude that you just don't know how to get started, so I'll confine myself to that.


a) how high was the palne at the moment the skydiver jumped?

Try  t = 0.

b) what is the skydiver's height above the ground after 12 seconds?

Try t = 12

c) what is the approximate time taken for the skydiver to reach  the ground.

Try H = 0 and solve for t.

d) How long does it take for the skydiver to reach a height of 900m above the ground? (Give your answer correct to one decimal place.)

Try H = 900 and solve for t.