Projectile Motion (1 Viewer)

[skillstriker]

How you do you know when a_y is negative or positive 9.8.

 

[ocatal]

It depends on the vertical direction of the projectile. If it is moving upwards, the acceleration will be negative since it is pushing it down. In other words, it is acting in the opposite direction. If it's moving downwards, the acceleration will be positive because they are (projectile and gravity) moving in the same direction.

Hope that helps

 

[braintic]

It depends on the vertical direction of the projectile. If it is moving upwards, the acceleration will be negative since it is pushing it down. In other words, it is acting in the opposite direction. If it's moving downwards, the acceleration will be positive because they are (projectile and gravity) moving in the same direction.

Hope that helps

Actually, it depends on which direction you arbitrarily decide is positive, regardless of the direction of motion of the projectile. Provided the velocity of the projectile obeys the same sign convention.

(And gravity doesn't 'move' - assuming that you did intend 'move' to be used as an intransitive verb.)

 

[Fizzy_Cyst]

Actually, it depends on which direction you arbitrarily decide is positive, regardless of the direction of motion of the projectile. Provided the velocity of the projectile obeys the same sign convention.

Exactly this. By convention, for 2-D projectile motion, upwards and right are positive, down and left are negative. Seeing as gravity is downward acceleration, it would be negative, however, if you choose downward as positive, then your acceleration would be positive.

Try and stick with one, dont mix it up as you will get confused. Try as use conventional methods snd stick with them, it becomes second nature after a while