finding speed of bullet using work energy theorem

Question

A bullet of mass 0.0385 kg is fired toward board with a thickness of 0.0225 m. Its speed is 375 m/s before making contact with the board and it passes through the board. The average force exerted on the bullet by the board has a magnitude of 746 N.

What is the speed of the bullet, in m/s, after passing through the board? (The weight of the bullet is negligible relative to the force exerted by the board. Assume the force exerted by the board is constant.)

Answer 1

A bullet of mass 0.0385 kg is fired toward board with a thickness of 0.0225 m. Its speed is 375 m/s before making contact with the board and it passes through the board. The average force exerted on the bullet by the board has a magnitude of 746 N.

What is the speed of the bullet, in m/s, after passing through the board? (The weight of the bullet is negligible relative to the force exerted by the board. Assume the force exerted by the board is constant.)

Hi Jule

mass m= 0.0385 kg

D= Thickness of plate = 0.0225 m

vi = 375m/s , vf =?

Deceleration = Average force/mass of Bullet = 746/0.0385= 19,376.62 m/s2 (Use Negative being deceleration )

vf² -vi² = -2aD

vf² =vi² + 2aD

vf² =

vf² = 375*375 -2*19376.62*0.0225

= 140625 - 871.95 = 139753.05

vf = sqrt (139753.05 )

=373.84 m/s ( approx)