Kinematic relations ( please please help me😭)

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    (Original post by Reihane)
    red ball is thrown straight up from the edge of the roof of a building. A green ball is dropped from the same point 1.80 seconds later. (a) If the height of the building is 60.0m, what is the initial velocity (ured) of the red ball, if both balls are to hit the ground at the same time ? Now consider the same situation, but let the initial velocity be a known quantity and the height of the building (h) be the unknown. (b) what must the height of the building be for both balls to hit the ground at the same moment, for the following values of ured​(i) 12.0 ms-1​​(ii) 19.1 ms-1 (c) If ured is greater than some maximum value umax there is no value of h that allows both balls to strike the ground at the same time.​(i) Determine the value of umax​(ii) There is a physical interpretation of this situation. What is it? (d) If ured is less than some minimum value umin there is no value of h that allows both balls to strike the ground at the same time.​(i) Determine the value of umin​(ii) There is a physical interpretation of this situation. What is it?
    There are several parts to this question. How have you attempted to answer it - show us your working and explain where you are having difficulty.

    Without that people will assume you are trying to get others to do your homework for you. Thanks.
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    (Original post by uberteknik)
    There are several parts to this question. How have you attempted to answer it - show us your working and explain where you are having difficulty.

    Without that people will assume you are trying to get others to do your homework for you. Thanks.
    Oh no, i have done part a and im on part b. The reason i pastedthe whole thing was to check if im doing it right. However part c and d are killing me, don't even understand what im being asked to do.
    For part a) i found time of red ball using displacement equation of green ball with Time as t-1.8 and its U=0, i got time as 5.3s then I substitute it into red ball's displacement equation to find U.

    Part b) using gren ball t = t-1.8 and red ball t=t . I used displacement equation of both into one equation and found Time to be 2.8s, im now going to use that to find s(displacement/height) and i included signs in every step except for finding time where signs cancelled out.
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    Im getting 2 different answers when I include signs in finding the time and when i dont.
 
 
 
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