Hi, these two questions have been boggling me for a week.. if anyone can I help I'd be very appreciative. The first one is.. A cylindrical rod of length 1.5 m and radius 0.02 m is insulated to prevent heat loss through its curved surface. One end is attached to a thermal reservoir at 573 K and another at 303 K. What is the rate at which entropy increaes for the rod-reservoir system? Now, when I saw rate I immediately thought dS/dt.. I've tried to solve it in numerous ways but I'm not sure what the correct way is. I first took the equation dS = dQ/T, and for dQ/dt = kA (Th-Tc)/L where k = 400 since it's copper. Anyway I got dQ = 90.48 dt. I then substituted this back into the dS equation and got dS = 90.48 dt/T, then I brought dt to make it dS/dt = 90.48/T.. but what do I plug in for T? Another way that I did this was take the equation delta S = Q/Tc - Q/Th I took the derivative of it with respect to time .. and got d(delta S)/dt = 1/Tc dQ/dt - q/Th dQ/dt and I subbed in dQ/dt and solved for d(delta S)/dt.. and I'm assumign this is wrong since you're finding the rate of change, of the change of entropy with respect to time. Other people I know just used S = dQ/T and then substituted S = dQ/Th + dQ/Tc and got an answer. however, this neither gives the rate of change.. And I just wanted to clarify that A is the cross sectional area under all circumstances, correct? And on to my 2nd question: Block 1 of mass 0.2kg is sliding to the right over a frictionless elevated surface at 8m/s. The block undergoes an elastic collision with stationary block 2. Assume that the spring does not affect the collision. After the collision, block 2 oscillates in Simple Harmonic Motion, with a period of 0.14 s, and block 1 slides off the opposite end of the surface landing at a distance d from the base of the surface after falling height 4.9 m. What is the value of d? So basically I talked to a teaching assistant who said that I was supposed to use the equation m1v1 = m1v1 + m2v2, but this makes no sense since if it's in a collision, wouldn't it transfer some of its energy towards the 2nd block? I'm having a hard time solving it.. basically I can find M2 and M1 from omega and the equation for period, but I'm still confused.