How to compute HP necessary to drive your vehicle?

Hi a little help with a noob here. I got myself a 2.16 HP dc motor and was planning on installing it on my tricycle which weighs 1000 lbs with baggage and passengers at least. Can anyone explain to me how to compute the necessary HP to make it move to a top speed of at least 50 kph?

I wont be able to test the DC motor because i would have to retro fit the shaft which would cost me. I want to make it work as much as possible.

thanks !

I badly need a response :frowning: I still have one week if i want to have the motor exchanged.