First we should find out how much time it takes.
This means the time it takes to fall those 500 meters. It starts at speed 0 vertically. 500=10t22500=10t22 so t=10 seconds.
Now the speed of 150 km/h should be expressed in meters per second. Divide that by 3.6. 150/3.6=41.66... or about 41.67. Now take this tenfold, you get 416.67. Rounding to 2 significant figures instead of 5 gives 420. Which I thought would be cool to mention.