X(t) = -4m - (9m/s)t + (2m/s^2) t^2 students make the following contentions abou

Question

X(t) = -4m - (9m/s)t + (2m/s^2) t^2 students make the following contentions about the motion during the first 2 seconds: "I think this object's instantaneous speed will increase with time since the ac positive". "No, the object will have a decreasing speed, since the acceleration is directed oppe the initial velocity." "I don't think we can tell what will happen to the speed from this equation, since it about the position as a function of time, not about speed or velocity."Which, if any, of these three students do you agree with? Nadeo Barrett Chinue None of them ease explain your reasoning.

Explanation / Answer

given x(t) = -4 - 9t + 2t^2

v(t) = dx/dt = -9 + 4t

at time t = 0

v = -9 m/s

at time t = 2s

v = -9 + (4*2) = -9 + 8 = -1 m/s

as the time passes the speed decreases

a(t) = dv/dt = 4

acceleration is positive

option madeo

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