Projectile motion clarification (1 Viewer)

[tom101007]

this is from a question in the 2001 3U maths exam, question 4, b(linky)

what i wanted to know was why you use the angle on the ground as 135, and not 45,

like when you use 45 you get a negative time, so its obviously wrong, but i just wanted to know why you would use 135 instead (and not just that 45+135=180)

 

[lyounamu]

this is from a question in the 2004 3U maths exam, question 4, b(linky)

what i wanted to know was why you use the angle on the ground as 135, and not 45,

like when you use 45 you get a negative time, so its obviously wrong, but i just wanted to know why you would use 135 instead (and not just that 45+135=180)

You use 135 degree because that's the degree it makes when it moves downwards. Alternatively you can use -45 degrees.

 

[tom101007]

ahhhhh, that makes sense, it has been bugging me for a while now

speedy reply too
thanks heaps