Answer:
This depends on what angle they are approaching each other before they collided.The two simple cases are if they are running in the same direction or opposite direction from each other. For either case, use the conservation of momentum equation to solve: M_total*V_result = M1*V1 + M2*V2
Explanation:
Here are two possible solutions.
Head-on collision: M1=78, V1=8.5, M2=72, V2=-7.5 (that's negative because he's running the other way), M_total = 78+72 = 150, so V_result = (78*8.5 - 72*7.5)/150 = 0.82 m/s. Sanity check, they weigh about the same and so most of their velocity should cancel out.
Running the same way: change the sign of V2 to positive so V_result = (78*8.5 + 72*7.5)/150 = 8.02 m/s. Sanity check, they weigh about the same and the resultant speed is between the two starting velocities.
<em>hope it helps:)</em>
Hello
Let's convert first the height from foot to meters:

This is the space covered by the ball in its accelerated motion, where the acceleration is the gravitational acceleration:

The law of motion is given by

Re-arranging, we can get the total time of the motion:

which is the time the ball takes to hit the ground.
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I hope I could answer part of your question
Answer:
34.292 m/s
Explanation:
When plane dives the gravitational acceleration becomes 10 times extra i-e
acceleration a = g= 10g's=10 ×9.8= 98 m/sec2
radius of dive circle = 12 m
v= speed= ?
Using

==>
= a × r = 98 × 12 = 1176
==> v= 
==> v= 34.292 m/s