After successfully clearing the bar during the pole vault, the vaulter falls to

Question

After successfully clearing the bar during the pole vault, the vaulter falls to the landing cushion while trying to calculate the impending impulse which will break his fall. If his mass is 78.4 kg and he has a velocity of -12.5 m/s just prior to landing, what is the linear momentum of the vaulter just prior to impact?

a. 6.27 kg. m/s b. -6.27 kg m/s c. -980 kg. m/s d. 980 kg. m/s

What is the average net force that the vaulter experiences after hitting the landing mat if it takes 0.31 secs to slow down to zero velocity?

a. 3161.3 N b. 3156 N c. 4005.5 N d. 2978.0 N

If the average net force was 5000 N, how long would it take the vaulter to slow down to zero velocity?

a. 0.1 s b. 0.2s c. 0.3s d. 0.4s

Explanation / Answer

(1). mass m = 78.4 kg

Velocity just prior to landing v = -12.5 m/s

the linear momentum of the vaulter just prior to impact P = mv

           P = 78.4 kg x -12.5 m/s

              = -980 kg m/s

(2). time t = 0.31 s

So, magnitude of the force F = P / t

                 = 980 / 0.31

                 = 3161.2 N

(3). Force F ' = 5000 N

Required time t = P / F

                       = 980 / 5000

                       = 0.196 s

                        = 0.2 s        ( two significant figures)

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