the spring is compressed by 7cm. How far must you compress a spring with twice the spring constant to store the same amount of energy?

If the heat engine is a perfect carnot cycle engine, thenefficiency = (t2-t1)/t2   where t1=temperature of cold reservoir ( ° k) = 135            t2=temperature of hot reservoir ( ° k)   = 325thereforeefficiency = (t2-t1)/t2 = (325-135)/325 = 0.5846 = 58%  note: this is the theoretical maximum efficiency of a perfect heat engine.   real-life engines do not achieve this value.

The density of the block of iron is lees than the density of mercury but the density of the block of iron is greater than the density of water

Number of electron i think

Electrical charge is measured in coulomb.(c). the amount of an electrical charge that moves in a circuit depends on the current flow and how long it flows for. a current of 10 a flows for 30 s,then 10 x=300 coulombs of electrical charge moves