Respuesta :
The displacement (in meters) of a particle moving in a straight line is given by:
[tex]s(t)=t^2-9t+15[/tex]The average velocity is defined as the division between the displacement and the time:
[tex]v_{\text{average}}=\frac{\Delta s}{\Delta t}[/tex](1)
For the time interval [3.5, 4]:
[tex]\begin{gathered} \Delta t=4-3.5=0.5 \\ s(3.5)=3.5^2-9\cdot3.5+15=-4.25 \\ s(4)=4^2-9\cdot4+15=-5 \\ \Rightarrow\Delta s=s(4)-s(3.5)=-0.75 \end{gathered}[/tex]Now, using the equation for the average velocity:
[tex]v_{\text{average}}=\frac{-0.75}{0.5}=-1.5\text{ meters per second}[/tex](2)
For the time interval [4, 5]:
[tex]\begin{gathered} \Delta t=5-4=1 \\ s(5)=5^2-9\cdot5+15=-5 \\ s(4)=4^2-9\cdot4+15=-5 \\ \Rightarrow\Delta s=s(5)-s(4)=0 \end{gathered}[/tex]Now, using the equation for the average velocity:
[tex]v_{\text{average}}=\frac{0}{1}=0\text{ meters per second}[/tex](3)
For the time interval [4, 4.5]:
[tex]\begin{gathered} \Delta t=4.5-4=0.5 \\ s(4.5)=4.5^2-9\cdot4.5+15=-5.25 \\ s(4)=4^2-9\cdot4+15=-5 \\ \Rightarrow\Delta s=s(4.5)-s(4)=-0.25 \end{gathered}[/tex]Now, using the equation for the average velocity:
[tex]v_{\text{average}}=\frac{-0.25}{0.5}=-0.5\text{ meters per second}[/tex](4)
For the instantaneous velocity, given the displacement equation, we have:
[tex]v(t)=2t-9[/tex]Now, for t = 4:
[tex]v(4)=2\cdot4-9=-1\text{ meter per second}[/tex]