Chapter 3.1, Problem 7PP

a.

To determine

The average acceleration of the bus while braking.

Answer to Problem 7PP

The average acceleration of the bus while braking is $a\text{=-8}{\text{.33 m/s}}^{-2}$.

Explanation of Solution

Given:

Initial velocity $u=25\text{ m/s}$

Final velocity $v\text{= 0 m/s}$

Time $t=3\text{}\text{ s}$

Formula Used:

Average acceleration is $a=\frac{v-u}{t}$

vis the final velocity

u is the initial velocity

t is the time.

Calculation:

  $a=\frac{v-u}{t}$

  $a=\frac{0-25\text{ m/s}}{3\text{}\text{ s}}$

  $a\text{=-8}{\text{.33 m/s}}^{-2}$

Conclusion:

The average acceleration of the bus while braking is $a\text{=-8}{\text{.33 m/s}}^{-2}$ .

b.

To determine

The average acceleration of the bus if it takes twice as long to stop.

Answer to Problem 7PP

The average acceleration of the bus while braking is $a\text{=-4}{\text{.167 m/s}}^{-2}$ .

Explanation of Solution

Given:

Initial velocity $u=25\text{ m/s}$

Final velocity $v\text{= 0 m/s}$

Time $t=6\text{ s}$

Formula Used:

Average acceleration is $a=\frac{v-u}{t}$

v is the final velocity

u is the initial velocity

t is the time.

Calculation:

  $a=\frac{v-u}{t}$

  $a=\frac{0-25\text{ m/s}}{\text{6 s}}$

  $a\text{=-4}{\text{.167 m/s}}^{-2}$

If it takes twice, the time to stop the acceleration will be halved.

Conclusion:

The average acceleration of the bus while braking is $a\text{=-4}{\text{.167 m/s}}^{-2}$.