An aeroplane lands on the runway with a velocity of 50 m/s and decelerates at 10 m/s^2 to a velocity of 20 m/s. Calculate the distance travelled on the runway.

Firstly, we note that the acceleration is constant, therefore this problem should be tackled with the SUVAT equations. Let's write down the information we have: s  we are asked to find this u = 50 m/s v = 20 m/s a = -10 m/s² (note that the plane is decelarating, hence the acceleration is negative!) t  no information about time Let's write down the SUVAT equations, that we should know by heart: v = u + at s = ut + ½at² s = ½(v + u)t v² = u² + 2as We have no information about t, therefore we will use the last equation. By inverting it we should come up with: s = 1/(2a) · (v² - u²) = 1/(2 · (-10 m/s²)) · (400 m²/s² - 2500 m²/s²) = 105 m In the end is always a good idea to make a couple sanity check: 1) Does the result have the correct unit of measurement --> Yes, meters is the unit of distance 2) Does the result seem intuitively reasonable? --> Yes We can now say we have solved the problem! :)