Propelling force due to an orifice

[Sia]

Homework Statement

A tank 1.5m high stands on a trolley and is full of water .it has an orifice of diameter 0.1m at 0.3m from the bottom of the tank.if the orifice is suddenly opened coefficient of discharge of the orifice is 0.60, then find propelling force on the trolley.
Ans: 67.39N

Homework Equations

F=c⋅ρ⋅A⋅v^2

The Attempt at a Solution

It looks like a simple problem based on Newton's third law of motion where the propelling force on the trolley must be equal to the change in momentum of the liquid jet coming out of the orfice.

thus F= 0.6X10^3X (Π/4)0.1^2X2X9.8X1.2
=110.35
which is not correct.

I am not getting what's wrong with my approach.

 

[Nidum]

What is the velocity of the flow through the orifice ?

 

[Sia]

What is the velocity of the flow through the orifice ? Why is this relevant ?

velocity of the flow will be: √(2gh)=√(2X9.8X1.2) =4.84
didn't understand next part