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Anit [1.1K]
3 years ago
6

Please help me with this (with explanation)

Physics
1 answer:
Sergeeva-Olga [200]3 years ago
6 0

Suppose the cyclist travels for a total time of <em>t</em> hours.

For 20 min = 1/3 hr, the cyclist does not move.

Over the remaining (<em>t</em> - 1/3) hr, the cyclist is moving at a constant speed of 22.0 km/hr, so that the cyclist would travel a distance of

<em>x</em> = (22.0 km/hr) • ((<em>t</em> - 1/3) hr) ≈ (22.0 km/hr) <em>t</em> - 7.33 km

If the cyclist's average speed over the total time <em>t</em> was 17.5 km/hr, then by the definition of average speed,

17.5 km/hr = <em>x</em> / <em>t</em>

Replace <em>x</em> with the distance expression from earlier:

17.5 km/hr = ((22.0 km/hr) <em>t</em> - 7.33 km) / <em>t</em>

Solve for <em>t</em> :

17.5 km/hr = 22.0 km/hr - (7.33 km) / <em>t</em>

(7.33 km) / <em>t</em> = 4.5 km/hr

<em>t</em> = (7.33 km) / (4.5 km/hr)

<em>t</em> ≈ 1.62963 hr

Then the distance the cyclist traveled must have been

<em>x</em> ≈ (22.0 km/hr) (1.62963 hr) - 7.33 km ≈ 28.5 km

and so the answer is A.

Alternatively, as soon as you arrive at

17.5 km/hr = <em>x</em> / <em>t</em>

you can instead solve for <em>t</em> in terms of <em>x</em>, then plug that into the distance equation.

<em>t</em> = <em>x</em> / (17.5 km/hr)

then

<em>x</em> ≈ (22.0 km/hr) (<em>x</em> / (17.5 km/hr)) - 7.33 km

<em>x</em> ≈ 1.25714 <em>x</em> - 7.33 km

0.25714<em>x</em> ≈ 7.33 km

<em>x</em> = (7.33 km) / 0.25714 ≈ 28.5 km

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