physics
posted by shirley .
an airplane has a takeoff speed of 80 meters per second which it reaches 35 seconds after starting from rest. What is the minimum length of the runway?

Start by calculating the acceleration of the plane as it moves from rest to takeoff. It gets up to 80 m/s in 35 seconds, so its acceleration is 80/35 m/s^2.
Now you can just plug in the formula for distance travelled under acceleration = ut + 0.5at^2.
Initial velocity u is zero. We've worked out the acceleration, and we know that t=35sec. The rest is easy.