7. It takes 1 second to hear the reflection of a loud noise made in front of a large barrier. If the speed of sound in air is 340 m/s, how far away is the barrier?
A. 85 m
B. 170 m
C. 340 m
D. 680 m

The material that keeps its new shape after it is stretched is called?

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.

Positrons are spontaneously emitted from the nuclei of