Solve Quadratic Equation for Cliff Height

  • Thread starter Thread starter frosty8688
  • Start date Start date
  • Tags Tags
    Freefall Motion
Click For Summary

Homework Help Overview

The problem involves determining the height of a cliff from which two stones are dropped and thrown downward at different times. The context is kinematics, specifically dealing with free fall and projectile motion under gravity.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the equations of motion for both stones, attempting to set up a relationship between their fall times and distances. Some express confusion about solving the resulting quadratic equation.

Discussion Status

There are varying calculations for the time it takes for the stones to hit the water, with participants providing different values for t. Some guidance is offered regarding the nature of the solutions to the quadratic equation, including the consideration of negative values.

Contextual Notes

One participant notes a simplification by using g=10 m/s² instead of the standard 9.81 m/s², which may affect the calculations discussed.

frosty8688
Messages
126
Reaction score
0
1. At t=0, a stone is dropped from the top of a cliff above a lake. Another stone is thrown downward 1.6 s later from the same point with an initial speed of 32 m/s. Both stones hit the water at the same instant. Find the height of the cliff.



2. d_{1}=\frac{1}{2}gt_{1}^{2}; d_{2}=v_{02}t_{2}+\frac{1}{2}gt_{2}^{2};d_{1}=d_{2}; t_{2}=t_{1}- 1.6s



3. \frac{1}{2}gt_{1}^{2}=v_{02}t_{2}+\frac{1}{2}g(t_{1}-1.6s)^{2}. \frac{1}{2}(9.81 m/s^{2})t_{1}^{2}=(32 m/s)(t_{1}-1.6s)+\frac{1}{2}(9.81 m/s^{2})(t_{1}-1.6s)^{2}. Here is where I get stuck in solving the quadratic.
 
Physics news on Phys.org
You should solve the equation yourself as it contains only maths. The equation will give you two values and i think one value of t1 will come negative which you must ignore.Try it :)
 
For some reason I get 2.82 seconds for t.
 
According to my calculation t comes to be 2.02 second
 
So height of cliff is 20m
 
Note i have taken g=10m/s^2
 

Similar threads

  • · Replies 21 ·
Replies
21
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K
Replies
6
Views
3K
Replies
13
Views
2K
  • · Replies 6 ·
Replies
6
Views
1K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
1K
Replies
1
Views
2K
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K