Monday, September 17, 2001

• If you have not already done so, remember to register on WebAssign by Wednesday.  The 10-day grace period has been extended to 30 days, but after this period, you will not be able to access WebAssign unless you have paid the registration fee on-line or with a User Access card (from the campus bookstore).
• Peer Tutoring Program offers free tutoring from 6:00 - 9:00 pm on Wednesdays, 2nd floor of Dey Hall
• A list of private tutors is available in the main Physics office (Phillips 278), fees are $15-25/hr.
• In addition to the RWP on the exam next week, you will write your own real-world problem (along with a solution), and this will count as 5% of your exam score.  Your problem will be graded based on the criteria for a good real-world problem.

Definition of force
Definition of mass

Newton's Laws of motion
    1)  Inertia:  A net external force is required to change an object's velocity.
    2)  F = ma:  a = F/m
    3)  Action/Reaction:  F₁₂ = F₂₁

Graph of a versus F:  what does the slope represent?

What is wrong with the free-body diagram of the football on page 81?

Definition of weight and "weightlessness":  F_g = w = mg

Show that objects in free-fall accelerate downward at  a = g

• #1 (P7) should be a straightforward application of F = ma and kinematics.
• #2 (P14) is similar to Example 4.1.  sum(Fx) = 0 and sum(Fy) = 0.  Find the angle first, then the weight.
• #3 (P25) is similar to Ex. 4.7.  Solve algebraically to find the tension and acceleration simultaneously (2 equations with 2 unknowns).  Be sure to watch the signs on your variables (+ and -) so they are consistent with whatever coordinate system you define.  Alternatively, you could also find the acceleration of the system (m1 + m2), where the net force is m2g, then find the tension by applying F = ma to m1.
• #4 (P41) is similar to the previous problem, but with friction and an angle added.  Be careful with the components and the signs.
• #5 (P43) is another statics problem.  Solve algebraically to find the answers.  The key here is recognizing that the normal force acting on each crutch is mg/4.

• HW4b
• RWP4 (due Friday)
• Create your own real-world problem for Exam 1 (due Monday).