ENGR 122
Homework 4
NOTE: Use engineering format for problems 1, 2 and 4. Use non-engineering format for problems 3, 5 and 6. This is
an individual assignment.
1. Find the moments about point A as requested below.
a. Find the moment of F1 about A. 420N-m CCW
b. Find the moment of F2 about A. 30N-m CCW
c. Find the moment of F3 about A. 0
d. Find the moment of F4 about A. 205N-m CW
e. Find the net moment of all forces about A. 245N-m CCW
F2=40N
F4=100N
60°
F1=60N
1m
7m
F3=50N
A
1m
1.5m
3m
2. Determine the net moment of the forces shown about point A assuming the crutch is 54 inches long. Denote
whether the net moment is clockwise (CW) or counter-clockwise (CCW). After setting up the problem, perform your
calculations using Mathcad, and show your Mathcad worksheet as part of your solution. 555 in-lbs CCW
3. Solve problem 2 again by building a function for the moment about point A as a function of the angle θ, where θ is
allowed to vary between 5˚ and 30˚. Show a plot of θ vs. M(θ) as well as your Mathcad worksheet in your solution.
4. A cyclist on a time trial bike exerts a pedal force as shown below. Determine the contribution of the 50 N force to
his total pedaling torque at the instant shown (find the moment of the 50 N force about the axis of rotation of the
pedal crank arm). 8.5N-m CW
HINT: It may be helpful to redefine the x-y coordinate system where x falls in line with the pedal crank.
5. Go to the Parallax web site and find a sensor that you think looks interesting (besides the one you found for the
last homework, the PING))) sensor, accelerometers, RFID sensors, and GPS sensors). Describe what the sensor
measures, some of the key specifications of the sensor, and the sensor cost.
6. Generate bug #4 for your “Bug List.” Remember that a bug can be something that doesn’t work quite right or that
could be improved, something that bothers you, or things that you notice others struggling with. For your homework,
please name the bug, write up at least a two sentence description of the bug, and provide pictures when it makes
sense to do so. You don’t need to try to find a solution to the problem at this point. Try to think of bugs in different
categories as you build your bug list. For example, find bugs related to major life activities (recreational, occupational,
tasks of daily living, transportation, communication, learning) and bugs affecting special people groups (disabled,
senior adults, children).
7. Bring one of your servos to class next time (already removed from the robot) along with a small screwdriver.