You are attending a county fair with your friend from your physics class. While walking around the fairgrounds, you discover a new game of skill. A thin rod of mass M = 0.505 kg and length = 2.70 m hangs from a friction-free pivot at its upper end as shown in the figure. Pivot Velcro M Incoming Velcro-covered ball m The front surface of the rod is covered with Velcro. You are to throw a Velcro-covered ball of mass m = 1.25 kg at the rod in an attempt to make it swing backward and rotate all the way across the top. The ball must stick to the rod at all times after striking it. If you cause the rod to rotate over the top position (that is, rotate 180° opposite of its starting position), you win a stuffed animal. Your friend volunteers to try his luck. He feels that the most torque would be applied to the rod by striking it at its lowest end. While he prepares to aim at the lowest point on the rod, you calculate how fast he must throw the ball to win the stuffed animal with this…

56 is not the correct answer!

81 SSM Figure 29-84 shows a cross section of an infinite conducting sheet carrying a current per unit x-length of 2; the current emerges perpendicularly out of the page. (a) Use the Biot-Savart law and symmetry to show that for all points B •P x B P'. Figure 29-84 Problem 81. P above the sheet and all points P' below it, the magnetic field B is parallel to the sheet and directed as shown. (b) Use Ampere's law to prove that B = ½µλ at all points P and P'.