A Very Fast Start

A car accelerates at a rate of a = t 2 m/s 2 a = t^2 \text{ m/s}^2 . At time t = 0 s t = \text{0 s} , the car is at x = 1 m x = \text{1 m} and the velocity v = 10 m/s v = \text{10 m/s} . Where is the car when t = 10 s t = \text{10 s} . Give your answer to the nearest tenth.


The answer is 934.3.

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2 solutions

Given that acceleration a = t 2 m/s 2 a = t^2 \text{ m/s}^2 , then velocity

v ( t ) = a ( t ) d t = t 2 d t = t 3 3 + C 1 where C 1 is the constant of integration. v ( 0 ) = C 1 = 10 v ( t ) = t 3 3 + 10 \begin{aligned} v(t) & = \int a(t) \ dt = \int t^2 \ dt = \frac {t^3}3 + C_1 & \small \blue{\text{where }C_1 \text{ is the constant of integration.}} \\ v(0) & = C_1 = 10 \\ \implies v(t) & = \frac {t^3}3 + 10 \end{aligned}

And displacement

x ( t ) = v ( t ) d t = ( t 3 3 + 10 ) d t = t 4 12 + 10 t + C 2 x ( 0 ) = C 2 = 1 x ( t ) = t 4 12 + 10 t + 1 x ( 10 ) = 10000 12 + 100 + 1 934.3 \begin{aligned} x(t) & = \int v(t) \ dt = \int \left(\frac {t^3}3 + 10 \right) dt = \frac {t^4}{12} + 10 t + C_2 \\ x(0) & = C_2 = 1 \\ \implies x(t) & = \frac {t^4}{12} + 10 t + 1 \\ x(10) & = \frac {10000}{12} + 100 + 1 \approx \boxed {934.3} \end{aligned}

In the problem statement, it starts at t = 1 t = 1 , rather than t = 0 t = 0

Steven Chase - 1 year, 4 months ago

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Thanks, I'll make the correction!!!

A Former Brilliant Member - 1 year, 4 months ago

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