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| <h3 id="back-link"><a href="../../#1.2">$\leftarrow$Back</a></h3> | | <h3 id="back-link"><a href="../../#1.2">$\leftarrow$Back</a></h3> |
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| <h3> Statement </h3> | | <h3> Statement </h3> |
| <p> | | <p> |
| $1.2.7.$ The bus moves for $20$ seconds in a straight line to the stop, passing a distance of $310$ m. Its initial speed is $15$ $\frac{m}{s}$. Prove that the velocity of the bus changes in direction. | | $1.2.7.$ The bus moves for $20$ seconds in a straight line to the stop, passing a distance of $310$ m. Its initial speed is $15$ $\frac{m}{s}$. Prove that the velocity of the bus changes in direction. |
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| <h3>Solution</h3> | | <h3>Solution</h3> |
| <p> | | <p> |
| Since the bus comes to a complete stop at the end, the average speed is | | Since the bus comes to a complete stop at the end, the average speed is |
| $$v_\text{average}=\frac{15+0}{2} \frac{m}{s}=7.5 \frac{m}{s}$$ | | $$v_\text{average}=\frac{15+0}{2} \frac{m}{s}=7.5 \frac{m}{s}$$ |
| If there is an equal-accelerated motion, then the body must travel a path | | If there is an equal-accelerated motion, then the body must travel a path |
| $$s = v_\text{average}\cdot t=150\text{ m}$$ | | $$s = v_\text{average}\cdot t=150\text{ m}$$ |
| Whence it follows that the body has accelerated, but the motion is not equal-accelerated | | Whence it follows that the body has accelerated, but the motion is not equal-accelerated |
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| <h4>Answer</h4> | | <h4>Answer</h4> |
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| The average velocity is greater than the initial velocity and the final velocity is zero. | | The average velocity is greater than the initial velocity and the final velocity is zero. |
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