Uma pedra é lançada do solo verticalmente para cima , ao fim de t segundos atinge a altura dada por H=40t-5t².?

S = 0 -2t^2 + 40t = 0 -t^2 + 20t = 0 t^2 - 20t = 0 t(t - 20) = 0 t' = 0 t'' = 20 O tempo total de ida e volta é de 20 segundos. O tempo levado para subir é igual ao tempo levado para descer. Portanto aos 10s o objeto atinge a altura maxima.

S = -2.(10^2) + 40.10 S = - 200 + 400 S = 200 Alternativa C.

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