In each of the following situations, draw a complete force diagram. That means, draw ALL the forces and ONLY the forces acting on the object I ask about. Choose conventional names for the forces: Think about which forces in your diagram you know the value of right from the start, and which you do not. Think about which of these latter "unknown" forces you COULD figure out, and how... (Assume that any "named" quantity mentioned specifically in the problem, like mass (m) or speed(v) or acceleration (a), is GIVEN to you as a number.)
(Answer links are at the very bottom)
1a) A race car, mass m, just after starting. It is moving to the right with speed (vi), and still accelerating (acceleration a). (Include friction)
1b) The same car, after it has reached top speed (vf) and is driving in a straight line at this constant top speed. (Include friction)
2a) A bullet, mass m, fired out of a gun pointed up at a 45 degree angle from horizontal, just after leaving the gun with speed (vi). (Ignore friction)
2b) Same as above, but including friction.
3a) A person in an elevator which is on its way UP (velocity vi) and is presently accelerating DOWN with magnitude a (in other words, on its way up but slowing).
The elevator system is complicated, and shown here: there is a cable with a counterweight (kind of like Atwood's machine), and also there is a piston under the elevator. But remember, your force diagram is only supposed to be for the person in the elevator.
3b) Same, but the person is holding a heavy briefcase, with mass Mb.
3c) Same as above, but draw the free body diagram for the briefcase.
4a) A pendulum, mass m, which is swinging, and has just reached its highest point at some angle "theta" from the bottom.
4b) Same pendulum at the same angle, but imagine that this one started with a larger swing, so at this point it is still on its way up.