This Chapter Was Not as Easy as You Thought
Be careful with this chapter. Most Physics C students say, “Oh, come on, this stuff is easy ... let’s move
on to something challenging.” Okay, you’re right—if you’re at the level you need to be for Physics C,
basic Newton’s second law problems need to be easy for you. What you must remember from this and the
equilibrium chapter is the absolute necessity of free-body diagrams.
No matter how easy or hard an F (^) net problem may seem, you must start the problem with a free-body
diagram. Points are awarded for the free-body diagram, and that diagram will ensure that you don’t make
minor mistakes on the rest of the problem. My own Physics C students frequently mess up on what should
be straightforward problems when they try to take shortcuts. If you draw the FBD and follow the four-step
problem-solving procedure, it’s hard to go wrong. Even professional physicists use free-body diagrams.
You must, too.
Practice Problems
Multiple Choice:
1 . A 2.0-kg cart is given a shove up a long, smooth 30° incline. If the cart is traveling 8.0 m/s after the
shove, how much time elapses until the cart returns to its initial position?
(A) 1.6 s
(B) 3.2 s
(C) 4.0 s
(D) 6.0 s
(E) 8.0 s2 . A car slides up a frictionless inclined plane. How does the normal force of the incline on the car
compare with the weight of the car?
(A) The normal force must be equal to the car’s weight.
(B) The normal force must be less than the car’s weight.
(C) The normal force must be greater than the car’s weight.
(D) The normal force must be zero.
(E) The normal force could have any value relative to the car’s weight.3 . In the diagram above, a 1.0-kg cart and a 2.0-kg cart are connected by a rope. The spring scale reads
10 N. What is the tension in the rope connecting the two carts? Neglect any friction.
(A) 30 N
(B) 10 N
(C) 6.7 N