A bullet is fired through a board 18.0 cm thick in such a way that the bullet's line of motion is perpendicular to the face of the board. The initial speed of the bullet is 420 m/s and it emerges from the other side of the board with a speed of 320 m/s. find
(a) the acceleration of the bullet as it passes through the board and (b) the total time the bullet is in contact with the board.

d=18cm=0.18m thickness of board

vi=420m/s speed before entering the board

vf=320m/s speed when leaving the board

vf²=vi²+2×a×d

Acceleration a=(vf²-vi²)/2/d

a=-205.5m/s².

As expected, a is negative because the bullet is decelerated.

vf=vi+a×t

t=(vf-vi)/a=(320-420)/(-205.5)= 100/205.5=0.486s

t=0.486s=486ms

its c i just checked it

i had this question and the answer was 3.15 miles.

martina travels from school to her mom's office. from there, she walks to school. after school, she walks to the library and then to a friends house before finally ending back at home. find martina's total distance traveled.

a) 0 miles  

b) 0.4 miles  

c) 1 mile  

d) 3.15 miles