1) A boy throws a stone up with a velocity of 60 m/s. How long will it take to reach the maximum height ( g = -10 m/s2 ) 2) A certain...

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1. The speed will decrease uniformly under the gravity force. The speed of decrease is g, i.e. the speed will be where is the initial speed and is a time in seconds ( is positive here).

The maximum height will be reached when the speed becomes zero. After that a stone will begin to fall down. The speed will be zero at

2. If a particle is in rest, then its weight is equal to gravity force, So the mass of a particle is

A mass remains unchanged regardless of the gravity force or other forces. As long as a particle remains the same (the same matter in the same quantity), its mass is preserved.

However, the weight due to gravity will be zero (no gravity = no force).