dennis@home wrote:

Say you have a cart travelling at 20 m/s with a wind behind it blowing
at 10 m/s

The relative wind at the cart is 10 m/s to the rear.

Now to stop the wind behind you have to accelerate the air going past
the cart to 20 m/s.

Who says you have to STOP the wind? You just need to SLOW it to some
extent, to do that you just have to accelerate SOME air past the cart.