Answer to Question #97814 in Mechanics | Relativity for C

Question

In vertical projectile motion,when the displacement is negative answer,does it mean it is below the point of reference?Why do sometimes final velocity also have a negative sign in front?Another question is in work energy theorem I also saw sometimes For Wnet calculations,let’s say friction of 1000 Ń was given,then they only put 1000N under Wnet,what about applied force and parallel force of gravity?does it mean if they don’t give us other information.we can just keep it simple and say Friction force is the only force under Wnet?

Answer 1

In vertical projectile motion, when displacement is negative it means it is below the point of reference

sometimes final velocity comes with negative sign it means the direction of final velocity is opposite to the positive direction of velocity which we assume

No, it is not true that we neglect applied and gravational force. Reality is that only friction is applied is such problems. For example work done in stopping a moving cart is done by the frictional force between tyre and ground when no external force is applied on it.