A cord is wrapped around a pulley that is shaped like a disk of mass m and radius r. The cords free end is connected to a block of mass M. The block starts from rest and then slides down an incline that makes an angle u with the horizontal as shown in Figure P10.92. The coefficient of kinetic friction between block and incline is m. (a) Use energy methods to show that the blocks speed as a function of position d down the incline is v 5 4Mgd 1sin u 2 m cos u 2 m 1 2M (b) Find the magnitude of the acceleration of the block in terms of m, m, M, g, and u.
Effect of molecular shape on electric forces (solution) 4.2.4.P11 The electric attractions and repulsions of the ions on the surface of co mplex molecules play a critical role in many biochemical reactions. An i nteresting component of some of these processes is that chemical reactions or elec tron transfers result in a change of the shape of a molecule, exchanging chemical energy for electrical energy, and resulting in a different surface configurati on and therefore different interactions. In this problem we will explore the effect of a change of configuration of a molecule on the force between it and an ion in a neighboring molecule. Consider the electric force between four ions on the surface of two larg e molecules as shown in the figure at the right. The heavy bl