http://www.ck12.org Chapter 5. Newton’s Laws
a. What is the weight of the stone?
b. What is the normal force acting on the stone?- The stone from the last question is now being pulled horizontally along the ground at constant speed in the
positivexdirection. Is there a net force on the stone? - A spring with spring constantk=400 N/m has an uncompressed length of 0.23 m. When fully compressed,
it has a length of 0.15 m. What force is required to fully compress the spring? - Measuring velocity is hard: for instance, can you tell how fast you’re going around the Sun right now?
Measuring acceleration is comparatively easy —you canfeelaccelerations. Here’s a clever way to determine
your acceleration. As you accelerate your car on a flat stretch, you notice that the fuzzy dice hanging from
your rearview mirror are no longer hanging straight up and down. In fact, they are making a 30◦angle with
respect to the vertical. What is your acceleration? (Hint: Draw a FBD. Consider bothxandyequations.) - Draw free body diagrams (FBDs) for all of the following objects involved (inbold) and label all the forces
appropriately. Make sure the lengths of the vectors in your FBDs are proportional to the strength of the force:
smaller forces get shorter arrows!
a. Amanstands in an elevator that is accelerating upward at 2 m/s^2.
b. A boy is dragging asledat a constant speed. The boy is pulling the sled with a rope at a 30◦angle.
c. Yourfootpresses against the ground as you walk.
d. Thepictureshown here is attached to the ceiling by three wires. - Analyze the situation shown here with a big kid pulling a little kid in a wagon. You’ll notice that there are
a lot of different forces acting on the system. Let’s think about what happens the moment the sled begins to
move.
a. First, draw the free body diagram of the big kid. Include all the forces you can think of, including
friction. Then do the same for the little kid.