This preview shows pages 1–2. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Chapter 6 solved problems 24. Picture the Problem : The spring stretches while the backpack remains at rest. Strategy: There are two forces acting on the backpack, the spring force to the left and the friction force to the right. The magnitudes of these two forces must be equal for the backpack to remain at rest. Use Newtons Second Law to relate the magnitudes of the forces and Hookes Law (equation 64) to find the spring force and hence the friction force. Solution: 1. (a) Write Newtons Second Law in the horizontal direction: x s x F f F ma = = = 2. Use Hookes Law to find the spring force and solve for the friction force. Note that the spring stretches in the negative x direction. ( 29 ( 29 150 N/m 0.0200 m 3.0 N s f F kx = =  =  = 3. (b) No, the answer to (a) doesnt depend on the mass of the backpack, it only depends upon the spring force and the fact that the backpack remains at rest. Insight: The static friction force changes with the applied force, always matching its magnitude until the maximum friction force is reached. If the applied force is increased even more, the backpack will slide (see the next problem). 35. Picture the Problem : The physical situation is depicted in the figure at right. The tension in the string between the two blocks is T 1 and the tension in the string that is tied to the wall is T 2 . A freebody diagram for the upper block 2 is also shown at right.. Strategy: Set the xaxis parallel to and pointing up the incline, and the yaxis perpendicular to the incline. Write Newtons Second Law in the x direction for each block and use the resulting equations to find T 1 and T 2 . The acceleration is zero everywhere in the system. Solution: 1. (a) Write Newtons Second Law for block 1 and solve for T 1 : ( 29 ( 29 1 1 block 1 1 1 2 1 sin sin 1.0 kg 9.81 m/s sin 31 5.1 N x F m g T T m g T =  + = = = = 2. (b) Write Newtons Second Law for block 2 and solve for T 2 : ( 29 ( 29 1 2 2 block 2 2 2 1 2 sin sin 5.1 N 2.0 kg 9.81 m/s sin 31...
View
Full
Document
 Spring '11
 BEAN
 pH

Click to edit the document details