PHY 物理 pre-asso的問題/_\教下我點做

The answer is very simple if you know the concept and the vertical position of the block, H1, which is not given here.

You first find the upward velocity (not speed, please don't make this fundamental mistake any more).

= 42 sin60 degrees (which is u, the inital velocity)

To calculate the time, t1, used before the stone reached its maximum height (where the final velocity, v, is zero), you apply the formula v= u +at
(what is 'a' here? you should know it).

You also use the formula s= ut + 1/2at ^2 to calculate the upward travel distance, h1.

With t1 calculated, the time that the stone travelled further before hitting the block t2, is 5.5 - t1., then you use the formula s= ut + 1/2at ^2 to calculate the vertical distance, h2, travelled downwards before the block was hit (u=0 here)

Question 1, the height of the cliff, H2,

= H1+h2 -h1
Q.2 (You need to ascertain whether you need to calculate the vertical or combined velocity)
Use the formula v = u + at to calculate the vertical velocity at time of hitting the block (remember you have the horizontal velocity (5.5cos 60 degrees) that remain unchanged), then calculate the combined velocity if necessary.

Q.3 The maximum height is h1 or h1 +H2 depending what the question is actually ask for (above the cliff or above the sea level).