A 7.80kg bullet moving at 575m/s strikes the hand of asuperhero causing the hand

Question

A 7.80kg bullet moving at 575m/s strikes the hand of asuperhero causing the hand to move 5.50cm in the direction of thebullets velocity before stopping a) Use work and energy considerations to find the averageforce that stops the bullet b) Assuming the force is constant, determine how much timeelapses between the moment the bullet strikes the hand and themoment it stops moving. Any help would be appriciated i'm not too sure what to do. Mybooks coming in the mail so I can't use my book for help. A 7.80kg bullet moving at 575m/s strikes the hand of asuperhero causing the hand to move 5.50cm in the direction of thebullets velocity before stopping a) Use work and energy considerations to find the averageforce that stops the bullet b) Assuming the force is constant, determine how much timeelapses between the moment the bullet strikes the hand and themoment it stops moving. Any help would be appriciated i'm not too sure what to do. Mybooks coming in the mail so I can't use my book for help.

Explanation / Answer

Mass m = 7.8 kg

Initial speed v = 575 m / s

Final speed V = 0

Work done W = change in kinetic energy

                       = ( 1/ 2) m[ V ^ 2 – v ^ 2 ]

                       = 1.289 * 10 ^ 6 J

Average force * displacement = 1.289 * 10 ^ 6 J

Average force = 1.289 * 10 ^ 6 J / displacement   where displacement S= 5.5 cm =0.055m

So, average force = 23.4444 * 10 ^ 6   N

(b). Accleration a = -F / m = -3.05 * 10 ^ 6 m / s ^ 2

So, required time t= ( V – v ) / a

                              = 191.3 * 10 ^ -6 s

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