The speed of the new-built regular tram is 5 km / h faster than the previous tram

| August 1, 2021 | education

The speed of the new-built regular tram is 5 km / h faster than the previous tram, so it covers the 20 km route 0.2 hours faster than the old tram. How long does it take for a new tram to pass this route?

1. The length of the tram route is: S = 20 km;

2. The speed of the old tram: Vc km / h;

3. His time on the route: Tc hour;

4. Speed of the new tram: Vn = (Vc + 5) km / h;

5. Its route time: Tn = (Tc – 0.2) hours;

6. Equation of movement of routes:

Tc – Tn = 0.2;

S / Vc – S / Vn = S / Vc – S / (Vc + 5) = 0.2;

5 * S = 0.2 * Vc * (Vc + 5);

0.2 * Vc² + Vc – 100 = 0;

Vc² + 5 * Vc – 500 = 0;

Vc1.2 = -2.5 + – sqrt ((- 2.5) ² + 500) = -2.5 + – 22.5;

A negative root is meaningless;

Vc = -2.5 + 22.5 = 20 km / h;

Vn = Vc + 5 = 20 + 5 = 25 km / h;

Tn = S / Vn = 20/25 = 0.8 hours.

Answer: a new tram passes the route in 0.8 hours.



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