a catcher catches a 90km/h fast ball. His glove compresses 4.5cm in bringing the ball to rest. How long does it take to complete a full stop?

t = 2x/V = 2*0.045*3,600/90 = 3.60 msec

90km/hr * 1000m/km *1hr/3600s = 25m/s

The kinetic energy of the fast ball = ½*m*Vi² = F*d = m*a*d

½Vi² = a*d = 0.045*a = 25²/2

a = 625/0.09 = 62,500/9

We know a is actually deceleration so "-a" is used below.

Vf = Vi - a*t = 0 so t = Vi/a = 25/(62500/9) = 0.0036s = 3600µs

OR

d = Vo*t - ½at² = 25*.0036 - 62500/18 * 0.0036² = 0.045m checks

t = 3.6ms or 3600µs <<<<<<<

90 km/hr x 1000 m/km x 1 hr/3600s = 25 m/s

4.5 cm = 0.045 m

v² = v₀² + 2ad

0 = 25² – 2a0.045

a = 6944 m/s²

d = ½at²

0.045 = ½(6944)t²

t = 0.0036 sec