Question

If a car can go from 0 to 60 mi/hr in 8.0 seconds, what would be its final speed after 5.0 seconds if its starting speed were 50 mi/hr?

Answer 1

$a= \frac{V}{t} \ \ \ \Rightarrow\ \ a= \frac{60\ [mi/hr]}{8\ [s]} \\ \\the\ final\ speed\ after\ 5.0\ seconds\\ \\V=50\ [mi/hr]+5\ [s]\ \cdot \frac{60\ [mi/hr]}{8\ [s]}=50\ [mi/hr] + \frac{5}{8} \cdot 60\ [mi/hr]=\\ \\=50\ [mi/hr]+37.5\ [mi/hr]=87.5\ [mi/hr]$

Answer 2

$v_1=60\ \frac{mi}{h}\\\\t_1=8.0\ s=\frac{8}{3600}\ h=\frac{1}{450}\ h\\--------------\\a=\frac{v}{t}\\\\a=\frac{60}{\frac{1}{450}}\ \frac{mi}{h^2}=27000\ \frac{mi}{h^2}\\--------------\\v_o=50\ \frac{mi}{h}\\\\t=5.0\ s=\frac{5}{3600}\ h=\frac{1}{720}\ h\\--------------$

$v=v_o+at\\\\\\v=50\ \frac{mi}{h}+27000\ \frac{mi}{h^2}\cdot\frac{1}{720}\ h=50\ \frac{mi}{h}+37.5\ \frac{mi}{h}=87.5\ \frac{mi}{h}\leftarrow Answer$