Answer:
The time which a car could accelerate from 0 to 70mph with a us=1.00 and uk=0.80 is
[tex]t=3.99s[/tex]
Explanation:
The net force knowing the accelerations must be determinate to get the speed goal
∑F=Fs-Fk=m*a
[tex]F_{s}=u_{s}*F_{N}=u_{s}*m*g[/tex]
[tex]F_{k}=u_{k}*F_{N}=u_{k}*m*g[/tex]
[tex]u_{s}*m*g-u_{k}*m*g=m*a[/tex]
[tex]a=(u_{s}-u_{k})*g[/tex]
[tex]a=0.80*9.8m/s^2[/tex]
[tex]a=7.84 m/s^2[/tex]
So knowing the acceleration and knowing the speed the car must get using equation of uniform motion accelerated
[tex]v_{f}=v_{i}+a*t[/tex]
[tex]70mph*\frac{1.60934km}{1mi}*\frac{1000m}{1km}*\frac{1h}{3600s}=31.29 \frac{m}{s}[/tex]
[tex]31.29 m/s=1.96m/s^2*t[/tex]
[tex]t=\frac{31.29m/s}{7.84m/s^2}[/tex]
[tex]t=3.99s[/tex]
