The earliest known Egyptian artifacts made from tin metal date back to approximately 1400 BC. If the smelting process for SnO2 occurs via the reaction sequence SnO2(s) + 2C (s) → Sn(s) + 2CO(g)

SnO2(s) + 2CO(g) → Sn(s) + 2CO2(g)

what is ΔHrxn for the conversion of SnO2 to Sn (s, white) by this smelting process? (Refer to Chapter 25 in the textbook for the heats of reaction.)

at its highest point (point a) the pendulum is momentarily motionless.  all of the energy in the pendulum is gravitational potential energy and there is no kinetic energy.  at the lowest point (point d) the pendulum has its greatest speed.  all of the energy in the pendulum is kinetic energy and there is no gravitational potential energy.  however, the total energy is constant as a function of time.