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I don't understand why r=-10 and not - 3 as it says height of 3m when using s=ut+0.5at^2.

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Reply 1

tonyiptony

So a question for you instead, if we're using s=3, how would you set up the equation?

Reply 2

davros

Original post by Vincent404

I don't understand why r=-10 and not - 3 as it says height of 3m when using s=ut 0.5at^2. image-419b93db-044a-46bf-8c20-0536bdacb9598906447221107352910-compressed.jpg.jpeg

Because they're trying to establish the components of the initial ('u' :wink:

velocity. The horizontal component is easy because there's no acceleration so they can just use distance / time, but for the vertical component the displacement after 2.5 seconds is -10 so that's what you use in the s = ut + (1/2)at^2 equation in the y- (or j-) direction.