91Ó°ÊÓ

Two circular rods, one steel and the other copper, are joined end to end. Each rod is 0.750 m long and 1.50 cm in diameter. The combination is subjected to a tensile force with magnitude 4000 N . For each rod, what are (a) the strain and (b) the elongation?

You pull horizontally on block B in Fig. E4.26, causing both blocks to move together as a unit. For this moving system, make a carefully labeled free-body diagram of block A if (a) the table is frictionless and (b) there is friction between block B and the table and the pull is equal in magnitude to the friction force on block B due to the table.

In a laboratory experiment on friction, a 135-N block resting on a rough horizontal table is pulled by a horizontal wire. The pull gradually increases until the block begins to move and continues to increase thereafter. Figure E5.26 shows a graph of the friction force on this block as a function of the pull. (a) Identify the regions of the graph where static friction and kinetic friction occur. (b) Find the coefficients of static friction and kinetic friction between the block and the table. (c) Why does the graph slant upward at first but then level out? (d) What would the graph look like if a 135-N brick were placed on the block, and what would the coefficients of friction be?

Figure E5.26

Two circular rods, one steel and the other copper, are joined end to end. Each rod is 0.750 m long and 1.50 cm in diameter. The combination is subjected to a tensile force with magnitude 4000 N . For each rod, what are (a) the strain and (b) the elongation?

When a batted baseball moves with air drag when does the ball travel a greater horizontal distance? (i) While climbing to its maximum height; (ii) while descending from its maximum height back to the ground; (iii) the same for both? Explain in terms of the forces acting on the ball.

A gyroscope is processing about a vertical axis. What happens to the precession angular speed if the following changes are made, with all other variables remaining the same?

(a) The angular speed of the spinning flywheel is doubled;

(b) The total weight is doubled;

(c) The moment of inertia about the axis of the spinning wheel is doubled;

(d) The distance from the pivot to the center of gravity is doubled.

(e) What happens if all the variables in parts (a) through (d) are doubled?

In each case justify your answer.

A tornado consists of a rapidly whirling air vortex. Why is the pressure always much lower in the centre than at the outside? How does this condition account for the destructive power of a tornado?

Compute the x- and y-components of the vectors $\stackrel{â‡\P Ä}{A}$,$\stackrel{â‡\P Ä}{B}$, $\stackrel{â‡\P Ä}{C}$and $\stackrel{â‡\P Ä}{D}$in Fig. E1.24.

A 0.150-kg toy is undergoing SHM on the end of a horizontal spring with force constant k = 300 N/m. When the toy is 0.0120 m from its equilibrium position, it is observed to have a speed of 0.400 m/s. What are the toy’s (a) total energy at any point of its motion; (b) amplitude of motion; (c) maximum speed during its motion?

A 0.60-kg book slides on a horizontal table. The kinetic friction force on the book has magnitude 1.8 N. (a) How much work is done on the book by friction during a displacement of 3.0 m to the left? (b) The book now slides 3.0 m to the right, returning to its starting point. During this second 3.0-m displacement, how much work is done on the book by friction? (c) What is the total work done on the book by friction during the complete round trip? (d) On the basis of your answer to part (c), would you say that the friction force is conservative or non-conservative? Explain.