Chapter 2, Problem 18P

To determine

The time to accelerate from 65 km/h to 120 km/h.

Answer to Problem 18P

Solution:

8.48 s

Explanation of Solution

Given:

Acceleration of the car, $a=1.8{\text{ m/s}}^{\text{2}}$

Initial velocity, $v_i=65\text{ km/h}$

Final velocity, $v_f=120\text{km/h}$

Formula Used: The time can be found from the first equation of motion:

  $v_f=v_i+at$

Calculation:

First,convert 65 km/h and 120 km/h to m/s.

  $\begin{array}{l}65\text{ km/h=}\frac{\text{65×1000}}{\text{60×60}}\text{=18}\text{.05 m/s}\\ 120\text{ km/h=}\frac{\text{120×1000}}{\text{60×60}}\text{=33}\text{.33 m/s}\\ t=\frac{v_f-v_i}{a}\\ t=\frac{33.33-18.05}{1.8}\\ t=8.48\text{ s}\end{array}$

Conclusion:

Accelerate from 65 km/h to 120 km/h automobile takes 8.48 s.