gravity homework

Assume that air resistance is negligible in these problems.

1.  Consider a baseball dropped from a height of 8-m. 
a.  How long should it take to hit the ground?
b.  What speed will it have immediately before impact with the Earth?

2.  You drop a rock from a bridge.  It takes 1.5 seconds to reach the water below.  How high above the water is the bridge?

3.  You throw a baseball straight up into the air with an initial speed of 25 m/s.
a.  How long does it take to reach apogee (highest point)?
b.  How high does it rise?
c.  How long would it spend in air before returning to your hand?

This one is trickier.  This is where it is important to consider signs and direction.  I suggest that you assign UP as the direction POSITIVE (which makes down negative). 

Three more related problems for this one:

d.  What would a graph of distance vs. time look like for this entire problem (up and down)?  Again, I suggest that you consider up to be positive.
e.  What would a graph of velocity vs. time look like for this problem?
f.  What would a graph of acceleration vs. time look like for this problem?

HW reminder

Hey folks. Just a reminder for homework:

Calculate the accelerations from your lab (informal) data. Get an average of all values.

Also, if you have time, think about these questions:

1. Should everyone get the same answer?

2. How does gravity change as your altitude increases?

3. How might gravity change as you go beneath the surface of the earth?

4. What would gravity be like at the center of the earth?

Motion homework

1. What do you notice is different about the 4(or 5) equations of motion?

2. Consider a car that goes from 0 to 30 m/s over a distance of 20 m.
A. What is the acceleration?
B. How long did this take?
C. What would a graph of distance vs. time look like for this scenario?
D. What would a graph of velocity vs. time
Look like for this scenario?

3. What is the acceleration due to gravity (g)? What does it represent?

HW

Next class, we will begin a new formal lab.  Hooray!

We will be comparing techniques for measuring speeds of motorized cars:

- photogate timer

An electronic timer with a light-gate - the timer records the amount of time for the object (car) to pass through the light beam.  The speed can be determined from that time and the width of the object.

- ticker tape timer

An electric timer that has paper tape pass through it.  It "clicks" 10 times per second and leaves a black dot on the paper tape.  The time between dots is 0.1 seconds.  By graphing the dots, the speed can be determined.

- stopwatch

Similar to what we just did in the informal lab.

Your task will be to compare the methods by percent different and try to judge which you think gives a more realistic picture of the car's speed.

Your homework - formulate a hypothesis:  Which method do you think is most accurate?  How will you know which is accurate?

homework

For next class:

Determine the average speeds associated with your data - for all of the objects, including yourself.

These values will likely be in m/s.

Show how to compute the values in miles per hour.  Describe how this conversion can be done.  Do not use an online conversion tool, unless it is to verify your results.

Also, find a good definition of "instantaneous velocity" by next class.

Hooray!

for Friday

Read about 2 of the following 3 technical devices:

microphones
telephone (the basics - the older voice box)
guitar pickups

Or look into something else cool that involved electromagnetic induction.

Yay!

topics for test

Electrostatics:

Coulomb's law
charge of electron / proton
inverse square law
electric field

Circuits:

current
voltage
resistance
power (recall light bulb problem)
series
parallel
combination circiuts

Magnetism

natural magnetism
electromagnetism
electromagnets
motors
right hand rule