Question

A plane can fly 540 miles with the wind in one hour less than it can fly 480 miles against the wind. The average wind speed is 30 miles per hour. Find the speed of the plane in still air.

Answer 1

Answer:

The speed of the plane in still air = 150 mph

Step-by-step explanation:

This is a relative velocity question

Let the velocity of the plane in still air be v

And let the time the plane can fly 480 miles against the wind be t

(Velocity of the plane relative to the wind) = (velocity of plane) - (velocity of wind)

Flying against the wind

(Velocity of plane relative to the wind) = (480/t)

(Velocity of the plane) = v

(Velocity of the wind) = 30 mph

(480/t) = v - 30

t = 480/(v-30) (eqn 1)

Flying with the wind

(Velocity of plane relative to the wind) = 540/(t-1)

(Velocity of the plane) = v

(Velocity of the wind) = -30 mph

540/(t - 1) = v + 30

t - 1 = 540/(v+30) (eqn 2)

Since t is equal in both cases, substitute the value of t in eqn 1 into eqn 2.

[480/(v-30)] - 1 = [540/(v+30)]

Multiply through by (v+30)(v-30)

480(v+30) - [(v+30)(v-30)] = 540(v-30)

480v + 14400 - (v² - 900) = 540v - 16200

480v + 14400 - v² + 900 = 540v - 16200

v² + 540v - 480v - 16200 - 14400 - 900 = 0

v² + 60v - 31500 = 0

Solving the quadratic equation,

v = 150 mph or v = -210 mph

We'll pick the positive answer because of the directions we have established.

Therefore, the speed of the plane in still air = 150 mph

Hope this Helps!!!