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Chapter 4: Forces & Newton's Laws
Example Questions & Problems
Fnet  F1  F2 
 Fn
a
Fnet
m
FAB  FBA
Example 4.1
a. Forces are shown on three objects. For each figure, draw and label the net (i) net force
vector and (ii) acceleration.
b. In the figures below, one force is missing. Use the given direction of acceleration to
determine the missing force and draw it on object.
Example 4.2
For each, draw a motion diagram, a force identification diagram, and a FBD..
a. An elevator, suspended by a single cable, has just left the tenth floor and is speeding up as
it descends toward the ground floor.
b. A rocket is being launched straight up. Air resistance is not negligible.
c. You've slammed on the brakes and your car is skidding to a stop while going down a 20°
hill.
d. A heavy box is in the back of a truck. The truck is accelerating to the right. Apply your
analysis to the box.
Example 4.3
 Draw a picture and identify the forces
 Draw a FBD for the object. Be sure to think carefully about the direction of Fnet & a.
Hint: Draw individual forces vectors with a black or blue pencil (pen). Draw the net force vector
Fnet with a red pencil (pen).
a. A heavy crate is being lowered straight down at a constant speed by a steel cable.
b. A boy pushing a box across the floor at a steadily increasing speed. Let the box be the
object for analysis.
c. A bicycle is speeding up down a hill. Friction is negligible, but air resistance is not.
d. You've slammed on your car brakes hill going down a hill. The car is skidding to a halt.
Example 4.4
The fastest pitched baseball was clocked at 46 m/s. If the pitcher exerted his force (assumed to
be horizontal and constant) over a distance of 1.0 m, and a baseball has a mass of 145 g.
a. Draw a FBD of the ball during the pitch.
b. What force did the pitcher exert on the ball during this record-setting pitch?
c. Estimate the force in part (b) as a fraction of the pitcher's weight.