Word problem: initial height of projectile

Click For Summary

Discussion Overview

The discussion revolves around a word problem involving the height of a projectile, specifically a ball thrown from a cliff. Participants explore how to determine the initial height of the ball using a quadratic equation that models its path.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant presents the equation h = -5t^2 + 5t + 210 and asks how to find the height of the cliff.
  • Another participant suggests setting t = 0 in the equation to find the height before the ball is thrown.
  • A later reply confirms the calculation, showing that when t = 0, h equals 210 meters, thus concluding that the cliff is 210 meters high.
  • One participant expresses uncertainty about how to use the information regarding the roots of the equation.

Areas of Agreement / Disagreement

There is agreement among participants that setting t = 0 yields the height of the cliff as 210 meters. However, there is a lack of clarity regarding the relevance of the root mentioned by one participant, which remains unaddressed.

Contextual Notes

Participants do not discuss the implications of the root -6 or its relevance to the problem, leaving that aspect unresolved.

mathdrama
Messages
20
Reaction score
0
A ball is thrown from a cliff. The path of the ball modeled by the equation
h = -5t^2+ 5t + 210,
where h is the height, in metres, of the ball above the ground, and t is the time, in seconds, after it is thrown. How high is the cliff?

Not really sure how to do this problem. I know that one of the roots is -6, but I don't know how to use this information.
 
Physics news on Phys.org
Re: word problem

mathdrama said:
A ball is thrown from a cliff. The path of the ball modeled by the equation
h = -5t^2+ 5t + 210,
where h is the height, in metres, of the ball above the ground, and t is the time, in seconds, after it is thrown. How high is the cliff?

Not really sure how to do this problem. I know that one of the roots is -6, but I don't know how to use this information.

Since $t$ is the time after the ball is thrown, you have to set $t=0$ at the equation to find the height of the ball before it's thrown, so when it is still on the cliff.
 
Re: word problem

So to make sure I have this right...

Let t = 0
h = -5(0^2) + 5(0) + 210
h = 0 + 0 + 210
h = 210
Therefore, the cliff is 210 meters high.
 
Re: word problem

mathdrama said:
So to make sure I have this right...

Let t = 0
h = -5(0^2) + 5(0) + 210
h = 0 + 0 + 210
h = 210
Therefore, the cliff is 210 meters high.

Yes, it is right! (Yes)
 

Similar threads

MHB Non-linear function with two unknown constants and one variable
  • · Replies 7 ·
Replies
7
Views
4K
projectile motion problem with no initial velocity given
  • · Replies 3 ·
Replies
3
Views
913
Find Projectile Flight Time Given Only Maximum Height
  • · Replies 4 ·
Replies
4
Views
3K
Find the height of a lamp based on the velocities of projectiles
  • · Replies 40 ·
2
Replies
40
Views
3K
Solving a Ball Thrown off a Cliff: How Long Does it Take?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Average Rate of Change Word Problem Help?
  • · Replies 1 ·
Replies
1
Views
4K
Projectile Motion Max Height and Range
  • · Replies 1 ·
Replies
1
Views
3K
MHB Molly's question at Yahoo Answers regarding projectile motion
  • · Replies 1 ·
Replies
1
Views
4K
Find the Height of a Building by dropping a ball from the top
  • · Replies 7 ·
Replies
7
Views
3K
Graduate Path of a projectile with a non-constant gravity
  • · Replies 5 ·
Replies
5
Views
2K