16. explain why is the sand
cooler under the umbrella
than outside the umbrella?

Here's what I get

Explanation:

The energy from the Sun's rays heats up the sand.

The umbrella prevents most of the Sun's rays from reaching the sand beneath it.

Thus, the sand in the umbrella's shadow receives less solar energy and heats up less.

hi there!

out of the two, (b) precision would be more reasonable.   however, both a and b could be pretty reasonable.

-awesomerepublic   : )

no. dot product   =0 when vecs at right angles