MECH325 - Homework Hints, Answers, and Extra Requirements

Homework 1 (Chapters 1 and 2)

TO ENHANCE YOUR LEARNING, PLEASE TRY TO WORK THE PROBLEMS FIRST WITHOUT LOOKING AT THE HINTS AND ANSWERS BELOW.

MAKE SURE YOU SATISFY ALL REQUIREMENTS LISTED BELOW AND IN THE ORIGINAL PROBLEM STATEMENTS (UNLESS INDICATED OTHERWISE BELOW).

NOTE - BECAUSE MOST ANSWERS ARE PROVIDED, IT IS VERY IMPORTANT THAT YOU SHOW ALL STEPS IN YOUR WORK.  THE GRADING WILL BE BASED ON THE COMPLETENESS, CLARITY, AND CORRECTNESS OF YOUR WORK, NOT JUST THE ANSWERS YOU PROVIDE.

1.32
[20 pts]
  • power = 0.0455 hp;  n = 191.0 rpm
1.37
[20 pts]
  • assume area is constant
  • express F(x) and integrate
  • work = 1.96 J
1.39
[20 pts]
  • assume the crankshaft speed is constant
  • the piston outputs work only during the 50 mm of the pressure stroke, the energy being provided by the flywheel
  • the motor is required to keep the flywheel up to speed, to replace the energy lost during the output stroke
  • the required input work (from the motor) is effectively averaged over the entire cycle (a complete revolution) by the flywheel
  • find the average input motor power and torque over an entire revolution
  • power = 3.75 kW;  torque = 19.89 Nm
2.18
[20 pts]
  • first draw all external forces and moments acting on the entire assembly (thrust force, propeller reaction torque, shaft torque, and flange reactions)
  • sum the moments about all three axes to find the unknown reaction moments at the flange
  • label all applied and reaction forces and moments (with appropriate directions) on the FBD
  • Mx = 40 NM;  My = 200 NM;  Mz = 20 NM;  Rx = 400 N
2.30
[20 pts]
  • sum moments about bearing A
  • a) FA = 60 N;  FB = 40 N;  MA = MB = 0
  • b) FA = 74 N;  FB = 24 N