Chapter 2, Problem 34P

To determine

The time taken by the car to attain the given speed.

Answer to Problem 34P

2.4 seconds.

Explanation of Solution

Given:

Initial velocity of the car $=v_i=0\frac{\text{m}}{\text{s}}$

Final velocity of the car $=v_f=85\frac{\text{km}}{\text{h}}=85\left(\frac{\text{1000m}}{\text{3600s}}\right)=23.6\frac{\text{m}}{\text{s}}$

Acceleration experienced by the car during free fall $=a=g=9.8\frac{\text{m}}{{\text{s}}^{\text{2}}}$

Time taken $=t$

Formula Used:

Acceleration is given as

  $a=\frac{v_f-v_i}{t}$

Calculation:

Substituting the values,

  $\begin{array}{l}9.8=\frac{23.6-0}{t}\\ t=\frac{23.6}{9.8}\\ t=2.4\sec \end{array}$

Conclusion:

Therefore, time taken by the car is 2.4 seconds.