Mastering Acceleration: Easily Solve for Time with this Simple Formula

[licorice]

Acceleration Help?

Homework Statement

a book is dropped from a had to the ground 1.5m, how long will it take to hit the ground?

Homework Equations

(v2)2 = (v1)2 =2ax?

The Attempt at a Solution

I am not sure if the equation is the correct one to use, and i am having trouble with the algebra part.

Homework Statement

Homework Equations

The Attempt at a Solution

 

[srmeier]

a book is dropped from the ground?

 

[licorice]

a book is dropped from the ground?

Sorry... from his hand to the ground.

 

[srmeier]

Look for a kinematic equation for position not velocity.

 

[llello]

So the equation you listed,

V^2 = V_o^2 +2a \Delta x

Has 4 variables, none of which are time. I suggest you look at the kinematic equations and select the one with all of the variables you have and need to solve for.

So the variables you already know (or can deduce) are what? (ie have numerical values for)

The variable you need to solve for is what?

 

[licorice]

Look for a kinematic equation for position not velocity.

what is a kinematic equation?

 

[srmeier]

My apologizes, llello is right.

 

[srmeier]

kinematic equation = equation of motion (this usage should be in your book)

 

[llello]

Kinematic equations are listed here.

http://www.physicsclassroom.com/class/1dkin/u1l6b.cfm

Its like the 2nd hit on google when you search for it.

 

[licorice]

So the equation you listed,

V^2 = V_o^2 +2a \Delta x

Has 4 variables, none of which are time. I suggest you look at the kinematic equations and select the one with all of the variables you have and need to solve for.

So the variables you already know (or can deduce) are what? (ie have numerical values for)

The variable you need to solve for is what?

I have distance, gravity, v1 and v2 and i am looking for time. Is it (v2)2 = (v1)2=2gy?

 

[licorice]

Kinematic equations are listed here.

http://www.physicsclassroom.com/class/1dkin/u1l6b.cfm

Its like the 2nd hit on google when you search for it.

thank you this helps.

 

[llello]

So a general way to go about kinematics problems:

- Note that in all of the equations only 5 variables appear: t, \Delta x, v, v_o, a
- These represent time, displacement, final velocity, initial velocity and acceleration.
- Each individual equation only contains 4 variables.
- Generally you are given 3 variables and want to solve for a 4th.
- Pick the equation that has the 3 known variables and the 4th unknown.
- Solve for the unknown.

- You may have to infer some things about the situation described. For example, it may tell you that you are on earth, so a = -9.8 m/s^2 (if you choose up to be the +y direction). Similarly, you may be told that an object reaches a maximum height before falling back down; at max height v = 0.

 

[Champdx]

You can use this formula S=ut+1/2at^2 and take a=9.8m/s^2. Since it is falling to ground the acceleration is positive.

 

[zgozvrm]

I have distance, gravity, v1 and v2 and i am looking for time. Is it (v2)2 = (v1)2=2gy?

Really? You have V2? What is it?