Need help with a physics concept?

Question

I'm having problems understanding the physics concept of velocity. Could someone help me get on the right path to answering this question?

Say a plane passes a stationary plane at 45 m/s. The arriving plane has a length of 36 m, and a passenger in the still plane can see the other plane out the window. How long can the person see the plane?

I know you're going to need the formula for velocity, but I don't know where to go from there.

Answer 1

The answer above is somewhat correct, but incomplete.

Its true that the position of a moving object is given by:
x = vt.
where x is position, v is the velocity, and t is time. However, in the problem you stated, how long the person in the still plane can see the moving plane is somewhat difficult to answer without some additional information.

For instance, you need to know the distance the moving plane has to travel to go from coming in to view to going out of view. That's an unknown by the way you've stated the problem. Though it appears from the problem that both planes are on the ground (at 45 m/s the moving plane is probably taking off or landing - unless it's a really small plane), you'd still have to know how much visibility the person in the still plane has outside.

If you have or can calculate the distance the moving plane is in view (let's call it 'd' for now), you put that in for x, and you have:
d (meters) = (45 m/s) * t (sec)
t = d/45 seconds.

Always remember to keep units straight. d should be specified in meters if the velocity is given in meters/sec. Then the answer would be in seconds.

The answer given by the person above would be the amount of time it takes for the plane to pass a particular point on the runway - not the amount of time it would be visible to someone. If the problem is really calling for how much time it takes to pass a point, then the problem is very poorly worded.

Answer 2

I agree with the above explination. Angular size is not accounted for. The farther away you are from the passing plane, the smaller and slower it will appear and therefore the longer it will be in view.

Bad question.

Answer 3

0.8

x=vt

36 for x, 45 for v