How can i use kinematic equations to solve this problem?

In summary, the conversation discusses a person's struggle with their homework on determining the duration of an object's flight. They mention throwing a stone off a tower and using equations to find the velocity and distance traveled. The acceleration is given as -9.81 m/s^2 and the person needs help finding all the necessary data to graph the results.
  • #1
kevin112996
1
0
Hello everyone,
This is my first post so I am sorry if this is in the wrong section. I am currently in a rush to finish my homework. I have tried working on it for several hours but I still cannot figure it out.
I am mainly trying to figure out how long the object will be in the air.

A stone is thrown upward at a speed of 30m/s off the edge of a 40m tall tower.

1. How can I find the velocity of the stone versus time. The time is suppose to start at 0 and go up increments of 0.3 sec from when the stone is thrown to the time the stone hits the ground.

Here are the equations I used: Final Velocity = Initial Velocity + Acceleration x Time
Distance = Initial Velocity x Time + 0.5 x Acceleration x Time^2
Final Velocity^2 = Initial Velocity^2 + 2 x Acceleration x Distance

I will have to graph this but I need to know how to find all the data first. Thank you for your help.
 
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  • #2
The accelaration is -g= -9.81 m/s^2 so the speed, after t seconds, is 30- 9.81t m/s. It's height will be 40+ 30t- (9.81/2)t^2 above the ground. Set that equal to 0 and solve for t. That is a quadratic equation and will have two roots, one of which is negative. That would be the time it was on the ground if you had thrown it up fast enough that it was still going at 30 m/s when it got 40 m above the ground.
 

1. How do I identify which kinematic equation to use for a specific problem?

When solving a kinematic problem, you must first identify the known and unknown variables. Then, you can use the appropriate equation based on the variables given. For example, if you are given initial velocity, final velocity, and time, you can use the equation vf = vi + at.

2. Can I use the kinematic equations for any type of motion?

Yes, the kinematic equations can be used for any type of motion as long as the acceleration is constant. This includes motion in a straight line, circular motion, and even projectile motion.

3. Is it necessary to memorize all of the kinematic equations?

No, it is not necessary to memorize all of the kinematic equations. You can derive them from the three basic equations: vf = vi + at, xf = xi + vit + 1/2at^2, and vf^2 = vi^2 + 2ax. However, it is useful to be familiar with the common equations and their variables.

4. What should I do if I encounter a problem with multiple unknown variables?

If you come across a problem with multiple unknown variables, you will need to use multiple kinematic equations and solve for each variable separately. Then, you can use algebraic manipulation to eliminate variables and solve for the final unknown.

5. Can I use the kinematic equations to solve problems with changing acceleration?

No, the kinematic equations can only be used for problems with constant acceleration. If the acceleration is changing, you will need to use calculus to solve the problem or break the problem into smaller segments with constant acceleration.

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