1. Physics 218: Mechanics Instructor: Dr. Tatiana Erukhimova Lecture 13

2. A block of mass 20 kg is pushed against a vertical surface as shown. The coefficient of friction between the surface and the block is 0.2. If θ=30 0, what is the minimum magnitude of P to hold the block still? θ P

3. Quiz (hw Ch 6) A block of mass m starts at rest at the point x=A, y=B. At time t=0 two forces begin to act on it: Here c 1, c 2, b 1 and b 2 are known constants. Where will the block be at any subsequent time, t?

4. 1. A crate of mass m is on the flat bed of a pick up truck. The coefficient of friction between the crate and the truck is . The truck is traveling at the constant velocity of magnitude V 1. Draw the free body diagram for the crate, if the crate does not slip. 2. The truck starts to accelerate with an acceleration a c. Draw the free body diagram for the crate, if the crate does not slip.

5. First exam Tuesday, September 29 105 Heldenfels Section 801 and half of 802 start at 7 pm Section 803 and half of 802 start at 8:10 pm

6. All liquids, gels and aerosols must be in three-ounce or smaller containers. No calculators and cell phones BRING YOUR STUDENT ID!

7. What is included? Chapters 1-6 Kinematics, vectors, Newton’s Laws

8. Kinematics

9. In components:

10. If is given, you can find and

11. Vectors

12. Newton’s 2nd Law

13. Newton’s 3rd Law N N

14. Problem 2 from Test 1 2008

15. Problem 3 from Test 1 2008

16. Problem 1 from Test 1 2008

17. Friendly advice DO NOT…

18. DO NOT use Const acceleration case formulas when acceleration is a function of time. You have to integrate or differentiate! What are the Const acceleration case formulas?

19. DO NOT write the vector sign over a projection!

20.  DO NOT forget that F p has two components: F p cos θ and F p sin θ

21. Do Not Forget to Write down what is given and express the answer in terms of what is given Box the answer Indicate the origin and positive x and y

22. Help Session: When: tonight at 7:10 pm Where: 206 James J. Cain Engineering/Physics Lab Building Spence St.

23. Have a great day! Hw: Be prepared for the test Good luck!