Equations of motion HW

The equations of motion are given above.  Try these problems.  Solutions will be coming over the weekend.  Thanks!

1.  (From last homework.)  How far will a freely-falling body fall in 4 seconds?  There is no air resistance.

2.  A car starts from rest and achieves a speed of 30 m/s in 4 seconds.  Find:

a.  the acceleration

b.  the distance that it goes in the 4 seconds

Now the same car applies the brakes once it has achieved 30 m/s.  If the car stops in 2 seconds, find:

a.  the acceleration

b.  how far the car travels in the 2 seconds

3.  Consider throwing a ball up in the air with an initial speed of 30 m/s.  I suggest that you call up positive (which makes gravity negative).

a.  How long will it take for the ball to reach apogee (the top)?
b.  How high will it go?

for next class (Friday)

1.  Find a definition for acceleration:  in words and in equation form.

2.  What are the units for acceleration?

3.  If an object starts from rest and achieves a velocity of 8 m/s in 10 seconds, what is the acceleration?

4.  If a car has an acceleration of 1.5 m/s/s, how fast is it traveling after 7 seconds (assuming that it starts from rest)?

5.  What is gravitational acceleration all about?  (Hint:  recall 9.8.....)

6.  If a ball is dropped from rest, how fast will it be traveling after 4 seconds?

7.  If a ball is dropped from rest, how far will it have fallen after 4 seconds?  (This is tricky - find the average velocity first.  We'll soon have equations to make this all easier.)

8.  See if you can find anything about "equations of motion" for homework.

Thanks!

Quiz postponed....

.... Until next week (Wednesday).

HW practice

Hey there,

FIRST THINGS FIRST:  Quiz in 2 classes - it will cover units, unit conversions and speed, etc.

Come up with a couple of conversions on your own and work through them.

Try a speed conversion first:  something like m/s to furlongs per fortnight, etc.  Be creative or weird.

If you're feeling ambitious, try a volume/time conversion:  something like liters/second to gallons/hour.

Also, find a definition for acceleration - in words, and in equation.

Thanks!

SL

For next class (Weds)

Work out your average speeds in m/s.

Think closely about all the errors in your methodology.  Write down all of the errors you can think of.

Also, some of you are still struggling with unit conversions.  Try to come up with 2-3 more of your own:  m/s to some other unit.  Work them all out.

Got it?

Thanks!

Fun problems

Here are some unit problems to play with:

1.  Create a factor to convert from m/s to light-years (LY) per millennium.  1 LY = 9.4607 x 10^12 km.

2.  Create your own conversion factor - m/s to something else interesting.

3.  How long is a micro-century?  Give your answer in units that are appropriate.   Also, micro equals 1 millionth.

4.  A good problem to think about.  If we gathered ALL of the people in the world together for the world's largest party, how large a social hall would we need to build?  Think about how to calculate this, and try it.  You'll have to make a couple of assumptions, of course.

For fun:

https://en.wikipedia.org/wiki/List_of_humorous_units_of_measurement

HW

HW for B block class:

Review the ideas of basic unit conversions.  Do these, looking up equalities as needed:

1.  10 inches = ____ m

2.  5 m = ____ km

3.  30 ft = ____ miles

4.  4 seconds = ____ hours


Now come up with your own "conversion factors", using the technique illustrated in class:

5.  1 m/s = ____ feet/year

6.  1 mile/hour = ____ feet/fortnight

* A fortnight is 14 days.

>

HW for C block class.

Play around with this.  It simulates the length of days (of sunlight) based on the day of the year.  It is related to the conversation we had today.

http://astro.unl.edu/naap/motion3/animations/sunmotions.swf


Also, we will be discussing unit conversions (now that you know a little about units).  Convert these units:

1.  30 inches = ____ feet

2.  30 inches = ____ yards

3.  30 inches = ____ miles

Recall that there are 5280 feet per mile.

4.  Now try this.  Usain Bolt is widely regarded as the fastest man alive.  He ran 200 m in 20.40 seconds, which is an average speed of 9.8 m/s.  Try to convert this speed to miles/hour.

You may need to know that there are 1609 meters in 1 mile.