Force is defined as the rate of change of momentum.
The initial amount of momentum is

because water stops when it hit the wall total change of momentum must be

.
Now let's calculate the force.

We need to find

. This is the amount of water hiting the wall per second.

Our final formula would be:

And now we can calculate the answer:
The Answer is= 7.8 x 10^4
Answer:
The speed is
and the direction is heading north.
Explanation:
In collisions the force exerted by the objects that collide is higher enough than the external forces that we can neglect that external forces, with that assumption we can use the conservation fo momentum law that states, final total momentum (pf) is equal initial total momentum (pi) if there’re not external forces or they are small enough to be neglected. Mathematically:

The total momentum is the sum of the momentum of each of the bodies we're dealing, in our case the moment of each car, then:

with pn the momentum of the 1000kg car heading north and ps the 800kg car heading south. Momentum is defined as mass times velocity, then:
(1)
It's important to note that when we talk about momentum and velocity direction matters, so we're are going to choose a system of reference where quantities pointing north are positive and pointing south are negative. So, the initial velocity of 1000 kg car is vni=5 m/s, initial velocity of 800 kg car is vsi=-4 m/s and the final velocity of 1000 kg car is vnf=-1 m/s. Now we can solve (1) for vsf and use the values we already have:

Because the sign is positive the direction is to heading north.
My teacher said 36m when I asked her
In my own words, I would say that physics is an area of science that seeks to explain and understand the fundamental nature of the dynamics of objects, essentially defining how objects can interact, in space and in time.