An airplane needs at least 145 meters of runway to take off. If the plane starts from rest and accelerates uniformly to a take-off speed of 170 km/hr then what is its acceleration in meters/second? How long does it take for the plane to become airborne?

User Icon for Steve Steve answered
13 years ago

First, get everything in the same units. The answer must be in m/sec^2, so we need to convert 170 km/hr to m/sec.

170 km/hr * 1000m/km * hr/3600sec = 47.222m/sec

Now, we know that it takes some time, t, to take off.

v = at
47.222 = at, so
t = 47.222/a

Distance s = 1/2 at^2
145 = 1/2 a (47.222/a)^2 = 2229.938/2a
290a = 2229.938
a = 7.69 m/sec^2

So, checking our answer

t = 47.222/7.69 = 6.14 sec

s = 1/2 * 7.69 * 6.14^2 = 144.955 m

Close enough for jazz.

User Icon for Explain Bot Explain Bot answered
1 year ago

To find the acceleration of the plane, we can use the formula:

acceleration = (final velocity - initial velocity) / time

First, let's convert the take-off speed from kilometers per hour (km/hr) to meters per second (m/s).

1 km/hr = (1000 m) / (60 s) = 16.67 m/s (approx.)

So, the take-off speed of 170 km/hr is approximately 170 * 16.67 = 2833.3 m/s.

Since the plane starts from rest, the initial velocity is 0 m/s.

Now we can calculate the time it takes for the plane to reach take-off speed.

We can use the equation of motion:

s = ut + (1/2)at^2

Where:
s = distance (145 meters)
u = initial velocity (0 m/s)
a = acceleration (unknown)
t = time (unknown)

By rearranging the equation, we have:

t^2 = (2s) / a

Substituting the known values:

t^2 = (2 * 145 m) / a
t^2 = 290 m / a

We can now find the time it takes for the plane to become airborne by calculating the square root of both sides:

t = √(290 m / a)

To find the acceleration, plug in the values of time (t = √(290 m / a)) and final velocity (v = 2833.3 m/s) into the acceleration formula:

2833.3 m/s = (final velocity) - (initial velocity)
= (a)(t)

So, the equation becomes:

2833.3 m/s = a * √(290 m / a)

To solve for acceleration (a), we need to square both sides to get rid of the square root:

(2833.3 m/s)^2 = (a * √(290 m / a))^2
8001208.89 = a^2 * (√(290/a))^2
8001208.89 = a^2 * (290/a)
8001208.89 = 290a

Now, solving for acceleration (a):

a = 8001208.89 / 290
a ≈ 27591.42 m/s^2 (approx.)

Therefore, the acceleration of the plane is approximately 27591.42 m/s^2.

Next, we can find the time it takes for the plane to become airborne by plugging this acceleration value into the equation for time:

t = √(290 m / a)
t = √(290 m / 27591.42 m/s^2)
t ≈ 0.0496 seconds

Therefore, it takes approximately 0.0496 seconds (or 49.6 milliseconds) for the plane to become airborne.