Đáp án:

Câu `23: `

`s = 2t^2+1/2t^4 `

`a = s'' = (2t^2+1/2t^4)'' `

`= (4t+2t^3)'`

`= 4+6t^2`

Tại `t = 4 -> a = 4+6.4^2 = 100 (m//s^2)`

Câu `24: `

`s(t) = 10 +0,5.sin(2πt+π/5)`

`a(t) = s''(t) = [10+0,5.Sin(2πt+π/5)]''`

`= [0,5 .(2πt+π/5)' .Cos(2πt+π/5)]'`

`= π .(2πt+π/5)' .-Sin(2πt+π/5)`

`= -2π^2 .Sin(2πt+π/5)`

`a(5) = -2π^2 .Sin(2π.5+π/5) ~~ -11,6 (m//s^2)`

Câu `25: `

`s(t) = 15+\sqrt{2}.sin(4πt+π/6)`

`a(t) = s''(t) = [15+\sqrt{2}.sin(4πt+π/6)]'' `

`= [\sqrt{2} .(4πt+π/6)' .Cos(4πt+π/6)]'`

`= [4π\sqrt{2}.Cos(4πt+π/6)]'`

`= 4π.\sqrt{2} .4π . [-Sin(4πt+π/6)]`

`= -16π^2 .\sqrt{2} .Sin(4πt+π/6)`

`a(3) = -16π^2 .\sqrt{2} .Sin(4π.3+π/6) ~~ -111,7 (m//s^2)`

Câu `26: `

`s(t) = -2t^2 +15t+3`

`v(t) = s'(t) = (-2t^2+15t+3)' = -4t+15`

`a(t) = v'(t) = (-4t+15) = -4`

`v(2) = -4.2+15 = 7 (m//s)`

`a(2) = -4 (m//s^2)`