To find the density of a substance you must know

Astring that is fixed at both ends has a length of 1.05 m. when the string vibrates at a frequency of 91.0 hz, a standing wave with five loops is formed. (a) what is the wavelength of the waves that travel on the string? (b) what is the speed of the waves? (c) what is the fundamental frequency of the string?

To do work, this truck uses energy stored in chemical fuel and an electrical battery. how much total energy does this truck put out?

Asteam power plant operates on an ideal reheat rankine cycle between the pressure limits of 15 mpa and 10 kpa. the mass flow rate of steam through the cycle is 12 kg/s. steam enters both stages of the turbine at 500°c. if the moisture content of the steam at the exit of the low-pressure turbine is not to exceed 10 percent, determine (a) the pressure at which reheating takes place, (b) the total rate of heat input in the boiler, and (c) the thermal efficiency of the cycle. also, show the cycle on a t-s diagram with respect to the saturation lines. (2.15 mpa; 45.0 mw; 42.6%)