The first law of thermodynamics states energy is not created or destroyed, so why must we ensure that the energy resources of the planet are conserved?

Crowbar of 5 metre is used to lift an object of 800 metre if the effort arm is 200cm calculate the force applied

Asheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200oc and is permitted to achieve a steady-state diffusion condition. the diffusion coefficient for nitrogen in steel at this temperature is 6 x 10- 11 m2 /s, and the diffusion flux is found to be 1.2 x 10-7 kg/m2 -s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3 . how far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3 ? assume a linear concentration profile.

The frequency of the fundamental of the guitar string is 320 hz. at what speed v do waves move along that string?