The reason why we can set both sides of the equation to p0 is because of the boundary layers that forms when a liquid comes into a contact with air. The deeper down we go in elevation, higher the pressure. Since we're assuming that tube isn't that tall, we can approximate the pressure in one...
The reason we can't use V=d/t directly is that the problem is a Projectile Motion Problem. In projectile motion we simplify the motion into 2 components (x,y). Since there was a initial velocity of 40 m/s, we expect the rock to "curve" due to the effect of gravity. Btw, it takes the same amount...
This is the same thing I typed and tried to explain. I included the formula for acceleration if you want to get more accurate results. How you interpret it, is up to the person of interest.
Sorry I was using the formula for velocity from my memory. The actual acceleration formula is (v^2-v0^2)/2*(x-x0)=a
X0 is initial distance and v0 is initial velocity. With proper assumptions one can work out the math. And we need acceleration to overcome static friction. If this was dynamic...
F= m(a+g*Mus)/(cos(theta)-Mus*sin(theta))
You will have to find acceleration a from 1D motion with constant acceleration. Or if you're computer literate then simple numerical computation will do the trick. As to answering the question, the value of F has to be larger than the expression above.