WEBVTT

00:00:03.650 --> 00:00:06.150
I'd like to talk to
you about solving

00:00:06.150 --> 00:00:07.920
these kinematics problems.

00:00:07.920 --> 00:00:10.730
So we're going to actually
start by asking ourselves

00:00:10.730 --> 00:00:13.210
three separate
questions anytime we

00:00:13.210 --> 00:00:15.276
start one of these
kinematics problems

00:00:15.276 --> 00:00:16.900
and this will help
us really figure out

00:00:16.900 --> 00:00:19.400
what's happening in the motion.

00:00:19.400 --> 00:00:21.330
So the first question
that we want to ask

00:00:21.330 --> 00:00:23.840
is, how many objects are moving?

00:00:23.840 --> 00:00:27.570
So do we care about more than
one object, and if we do,

00:00:27.570 --> 00:00:30.180
we need to make sure to
label each one distinctively.

00:00:30.180 --> 00:00:32.180
We also want to know how
many dimensions we need

00:00:32.180 --> 00:00:35.240
to care about for each object.

00:00:35.240 --> 00:00:37.460
The second question that
we want to ask ourselves

00:00:37.460 --> 00:00:40.980
is, how many stages of
motion does each object have?

00:00:40.980 --> 00:00:43.110
So for an example,
if you're told

00:00:43.110 --> 00:00:45.530
that a bicycle is
initially accelerating

00:00:45.530 --> 00:00:48.110
and then, at a certain
time, it stops accelerating,

00:00:48.110 --> 00:00:50.470
then you know that that
initial acceleration

00:00:50.470 --> 00:00:52.730
is going to have different
equations of motion

00:00:52.730 --> 00:00:54.890
than the point in
time where it now has

00:00:54.890 --> 00:00:58.290
an acceleration equal to zero.

00:00:58.290 --> 00:01:00.400
The final thing that
we want to think about,

00:01:00.400 --> 00:01:03.720
we want to figure out what
special conditions there are.

00:01:03.720 --> 00:01:07.910
So for example, you might be
told that the cart is initially

00:01:07.910 --> 00:01:08.670
at rest.

00:01:08.670 --> 00:01:10.600
So what does that
mean in reality?

00:01:10.600 --> 00:01:15.210
It means that you can write
down something like, v of 0

00:01:15.210 --> 00:01:18.370
is equal to 0, that's
what it means for the cart

00:01:18.370 --> 00:01:19.780
to initially be at rest.

00:01:19.780 --> 00:01:25.250
v cart is-- v at
time 0 is equal to 0.

00:01:25.250 --> 00:01:27.310
So those are the kinds
of special conditions

00:01:27.310 --> 00:01:29.560
that you need to pay
attention for in the problem

00:01:29.560 --> 00:01:31.520
and that will help
you figure out--

00:01:31.520 --> 00:01:33.900
get all of the numbers
or the variables

00:01:33.900 --> 00:01:36.270
that you need to
solve your equation.

00:01:36.270 --> 00:01:38.664
Once you're done thinking
through these different steps,

00:01:38.664 --> 00:01:40.039
the final thing
you should always

00:01:40.039 --> 00:01:45.490
do before starting a problem
is draw out your problem,

00:01:45.490 --> 00:01:49.360
properly label your
system, and then of course

00:01:49.360 --> 00:01:56.650
draw your origin, your
axes, and your unit vectors.

00:01:56.650 --> 00:01:58.620
And this way, it
will be easy for you

00:01:58.620 --> 00:02:02.640
to organize all of the different
information that you have.