Chapter 5: Applying Newton's Laws
Fx  max
Example Questions & Problems
Fy  may
(mg, fS  μSN, fk  μkN, D  41 ρAv 2 )
Example 5.1
The figures show FBDs for an object of mass m. Write the x- and y-components of Newton's
second law. Write your equations in terms of the magnitudes of forces F1, F2, ... and any angles
defined in the diagram.
ma x   Fx 
ma y   Fy 
ma x   Fx 
ma y   Fy 
Example 5.2
The three ropes are tied to a small, very light ring. Two of these ropes
are anchored to walls at right angles with the tensions shown in the
figure. What are the magnitude and direction of the tension T in the
third rope?
Example 5.3
The figure shows two 1.00 kg blocks connected by a rope. Assume the rope is massless.
The entire assembly is accelerated upward at 3.00 m/s2 by force F.
a. What is F?
b. What is the tension of rope?
Example 5.4
Bonnie and Clyde are sliding a 300 kg bank safe across the floor to their getaway car. The safe
slides with a constant speed if Clyde pushes from behind with 385 N of force while Bonnie pulls
forward with a rope with 350 N of force. What is the safe's coefficient of kinetic friction on the
bank floor?
Example 5.5
a. A 0.60 kg bullfrog is on a log tilted 30o above horizontal. How large is the normal force on
the log on this bullfrog?
b. A 4000 kg truck is moving at constant velocity up a 15° slope. How big is the friction force on
the truck?