Question 5
Why are equal forces always applied to the two Newton balances A and B in activity 3?
The right answer is the one marked above.
To stop the wooden strip turning, so that it stays at rest. If the strip is not at rest the resultant cannot be read off C.
Unequal forces on A and B set the strip turning. This is not a question of how easily the balances can be read but of whether the activity works at all. And C's reading must not be zero — that is the resultant.