Brian is attempting to high jump over a crossbar set at 2.13 m (7.0 ft). At the instant of takeoff (when he is no longer in contact with the ground), his vertical velocity is 4.2 m/s and his center of gravity is 1.25 m high. What is Brian's vertical acceleration at the instant of takeoff?

His verticak acceleration is 10.02m/s²

Explanation:

Given u = initial velocity = 4.2m/s

H = 2.13m and h =1.25m initial height

At the point where he reaches the crossbar he is no more moving upwards and has reach the maximum height where his final velocity V is 0

So usnng the relation V² = U² + 2a(H - h)

0 = 4.2² + 2a(2.13 - 1.25)

1.76a = 17.64

a = 10.02m/s².

Please note that it is the center of gravity of Brian that is used to measure how high he has jumped.