Question 4
When one object was hung from a Newton balance the reading was 80 N. When another object of mass 500 g was hung as well, what is the resultant force pulling the Newton balance down, in newtons? (Take g = 10 m s−2.)
The right answer is the one marked above.
85 N. 500 g = 0.5 kg, so its weight is 0.5 kg × 10 m s−2 = 5 N. Both weights act downwards, so 80 N + 5 N = 85 N.
580 N comes from adding 500 itself — a mass is not a force; it becomes one only after multiplying by g. And since both weights act the same way, nothing is subtracted.