posted by kulani .
A tennis ball of mass 100g is dropped from a height of 40m.It hits the ground and bounces back to a height of 30m after an impact of 0,01s.Ignore the air resistance .what was the velocity of the ball when it hit the ground ?
You have more information than you need to answer this question. The time to fall does not depend upon the mass, or how high it bounces, or the contact time. The "fall time" is simply
t = sqrt(2H/g)= 2.86 seconds
Are there other parts of the question that require the other information (such as the average force on the ground during a bounce)?