Tina knows that sonar measures distance by timing how long the echo of a sound takes to return. She says it is possible because sound has a particular frequency. Is she correct?

Henry, whose mass is 95 kg, stands on a bathroom scale in an elevator. the scale reads 830 n for the first 2.4 s after the elevator starts moving, then 930 n for the next 2.4 s. part a what is the elevator's speed 4.8 s after starting? express your answer with the appropriate units.