1 question (urgent)

this is physics projectile question,
you can divide the equation into the deriving part,
and solve the u into 3 equation.
anyway, i solve this long equation to you as follow

4 = 80 (tan 60') - [10(80)^2] / [2u^2 (cos 60')^2]

80√3 - 4 = 64000 / [2u^2 (cos 60')^2]

80√3 - 4 = 32000 / [u^2 (1/4)]

80√3 - 4 = 128000 / u^2

u^2 = 128000 / (80√3 - 4) = 951.219781

so, u = 30.84 ms^-1

Hope I can help you, 希望幫到你 :)

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