# Dynamics Help. My exam is on Monday

#### jessica4002

Dynamics Help. My exam is on Monday!!!

My Dynamic's Unit Exam is on Monday and I need help! Last week I had my Kinematic's Unit Exam and my written was something like:

How do you find the acceleration of a runner running the 100m sprint? Draw a sketch, list all the formulas you're going to use, do a sample calculation (make up some reasonable numbers), and a brief discussion of where some errors could occur.

My teacher said my Dynamic's written will be exactly the same thing, but I need help because how do I measure the force, power, kinetic energy, etc, using "classroom" type materials? We never did any labs.

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#### HallsofIvy

Homework Helper
How is acceleration defined? Do you think the runner will have constant acceleration or will it change? What formulas do you know that have anything to do with acceleration?

#### amt

Is the acceleration you are going to find the average acceleration or Instantaneous acceleration? The runner could be changing velocity during his 100m sprint. This would suggest changing acceleration. Change in Velocity with respect to time is acceleration: a= dv/dt.

If you want to find his acceleration at any particular point in time(say his acceleration at 50m when t=5 seconds) then it would be instantaneous acceleration. If you simply want to find the total of all such accelerations over the entire 100m, then that would be the average acceleration.

Acceleration is also the second derivative of 'x' with respect to 't' : a=d^2x/dt^2

Try playing with the formulas x=x0+v0t+1/2at^2 and v=v0+at. Both these formulas show a relationship between 'a','v' and 't'.

#### jessica4002

Well, my Kinematics written was easy, it gives you 100m, so I just made up 10 seconds, put it into v=d/t, then a=v/t and I'm done!

The written also asks for what materials I have to use, so meter stick, stopwatch, etc, that stuff.

I'm just confused with my Dynamics written. What materials do I put down if I want to measure force, pressure, etc?

#### Maxos

Where are you from?

#### jessica4002

No one in this forum knows how to measure force, power, etc using "classroom" type materials?

For example: to measure time, I would use a stopwatch!

#### amt

F=ma.

A weight scale is one instrument along with the stop watch.

#### EnumaElish

Homework Helper
jessica4002 said:
What materials do I put down if I want to measure force,
A scale. Think of the punching bag and the sledgehammer strike in an entertainment park. Each has a scale that shoots up when hit. http://www.savage-ent.com/fun_fair/strikers.htm [Broken]

pressure,
A barometer, maybe?

From physics glossary: "Power is the rate of working. Work is done on an object whenever it moves because it is pushed or pulled. Work increases the energy of the object. An increase in energy may heat up the object, speed it up, lift it up, or all of the above." COnclusion: depending on the type of energy, you may need a thermometer (heat), a meter (speed or lift) and a watch (time).

I hope this is (still) useful.

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