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5. The function $Q = 0.003 t^{2} - 0.625 t + 25$ represents the amount of energy, in Joules, in a battery after t minutes of use.
a) State the amount of energy held by the battery immediately before it was used. [1]
$\begin{aligned} Q & = 0.003 t^{2} - 0.625 t + 25 \\ = 0.003 (0)^{2} - 0.625 (0) + 25 \\ Q & = 25 \end{aligned}$
b) Calculate the number of minutes it takes for the energy to reach zero. [4]

Answer

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Answer

$b) 53.99 minutes$

Steps

Step 1 ： $Q = 0.003 t^{2} - 0.625 t + 25$

Step 2 ： $Q = 0.003 (0)^{2} - 0.625 (0) + 25$

Step 3 ： $Q = 25$

Step 4 ： $0 = 0.003 t^{2} - 0.625 t + 25$

Step 5 ： $t \approx 53.99$

Step 6 ： $a) 25 Joules$

Step 7 ： $b) 53.99 minutes$