18. A hot plate, a large beaker of water, and grains of rice are used in a class demonstration. When the water begins to boil, the rice moves in a circular pattern. The model demonstrates -

where are the vectors ?

the part of the wave he is travelling on is the crest

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.