Final answer:
The instantaneous acceleration at time t=12s is -100 m/s^2.
Step-by-step explanation:
To find the instantaneous acceleration at time t=12s, we need to find the derivative of the velocity function with respect to time. The velocity function is given as v(t) = 20t - 5t^2 m/s. To calculate the derivative, we can use the power rule of differentiation. Taking the derivative of the velocity function, we get a(t) = 20 - 10t m/s^2.
Now we can substitute t=12s into the acceleration function to find the instantaneous acceleration at that time. a(12s) = 20 - 10(12) = -100 m/s^2.
Therefore, the instantaneous acceleration at t=12s is -100 m/s^2.