Asound wave with a frequency of 400 hz is moving through a solid object. if the wavelength of the sound wave is 8 m, what is the speed of sound traveling through the solid object?

50 m/s
3200 m/s
408 m/s
0.02 m/s

Will you chech and finish these for me, because i am stumped with them.

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.

You've already seen the value of 9.8 in this lesson. what's this value called? what quantity does it represent?