1. Homework (due Monday) Section 4.5, 4.6 (Examples!!!!) Problems (p.111) #20, 32, 35, 36, 40, 45 A block of mass m is projected with an initial speed v 0 along the horizontal plane with coefficient of kinetic friction μ k and of static friction μ s. How far will the block go until it stops?

2. Does the coefficient of friction depend on the mass of the block? Does the force of friction depend on the mass of the block?

3. I push (with force Fext) on a block (mass m) which sits on the table. The block is not moving, because there is static friction (coefficient  s ). What can you say for sure about the frictional force, f? A: f =  s mg B: f = Fext C: f > Fext D: f < Fext E: Not enough information (or, MORE than one of the above)

4. 10kg T=98N

5. aa a 10kg 5kg

6. 10kg 5kg x y W1W1 W2W2 TT T T xy T0T W1W1 0-m 1 g ma0-m 1 a xy T0T W2W2 0-m 2 g ma0m2am2a Object 1 Object 2 xy T W1W1 ma xy T W2W2 T – m 1 g = -m 1 a T – m 2 g = m 2 a a a T T T = m 1 g-m 1 a T = m 2 g+m 2 a aa a

7. 10kg 5kg W1W1 W2W2 T T m1gm1g m2gm2g T T m1m1 m2m2 Pulleys Check the units! Check the limiting cases!

8. 10kg 5kg W1W1 W2W2 T T a m1gm1g m2gm2g m 1 +m 2 m 1 g - m 2 g = (m 1 + m 2 )a m1m1 m2m2 m1gm1g m2gm2g T T Pulleys

9. Pulleys and Atwood machine m1m1 m 2 T – m 1 g = -m 1 a T – m 2 g = m 2 a a a T T T = m 1 g-m 1 a T = m 2 g+m 2 a T = ?

10. Quiz m1m1 m 2 1.Draw a free body diagram for a)block 1 b)block 2 2.Draw an acceleration vector for each block 3.Set Cartesian coordinates 4.Find all x and y components of all forces and the accelerations for the both blocks separately!!! 5.Write down Newton’s Second Law for the components 6.Find the acceleration A block 1 and block 2 are connected by a light string that passes over frictionless pulley, as shown on the figure. There is NO FRICTION between block 1 and the surface of the table.