Here's an interesting challenge you can give to a friend. hold a $1 bill by the upper corner. have a friend prepare to pinch the lower corner, putting their fingers near but not touching the bill. tell them to try to catch the bill when you drop it simply by closing their fingers. it seems easy but it isn't. it would take them about 0.25 seconds to react and close their fingers— which isn't fast enough to catch the bill. how much time does it take for the bill to fall beyond her grasp? the length of the bill is 16cm.

Explain the doppler effect in terms of frequency, wavelength, and speed.

Ablock of mass m = 2.5 kg is attached to a spring with spring constant k = 790 n/m. it is initially at rest on an inclined plane that is at an angle of 28 degrees with respect to the horizontal, and the coefficient of kinetic friction between the block and the plane is k = 0.14. in the initial position, where the spring is compressed by a distance of a = 0.18 m, the mass is at its lowest position and the spring is compressed the maximum amount. take the initial gravitational energy of the block as zero. b) if the spring pushes the block up the incline, what distance, l, in meters will the block travel before coming to rest? the spring remains attached to both the block and the fixed wall throughout its motion.

The 10-kg double wheel with radius of gyration of 125mm about o is connected to the spring of stiffness k = 600 n/m by a cord which is wrapped securely around the inner hub. if the wheel is released from rest on the incline with the spring stretched 225 mm, calculate the maximum velocity v of its center o during the ensuing motion. the wheel rolls without slipping