A 1-kg rock that weighs 10 N is thrown straight upward at 20 m/s. Neglecting air resistance, the net force that acts on it when it is half way to the top of its path is
A)less than 10 N.
B)10 N.
C)more than 10 N.

Question

Quizplus · Accepted Answer

When the rock is thrown upward, the only force acting on it is the gravitational force, which is equal to its weight of 10 N. As the rock moves upward, this force gradually decreases until it reaches zero at the highest point of its path (where its velocity is momentarily zero). 
Halfway up, the force is still equal to its weight of 10 N, as there are no other forces acting on it. Therefore, the net force on the rock when it is halfway up is also 10 N.

A 1-Kg Rock That Weighs 10 N Is Thrown Straight