- #1

epiccy

1. Homework Statement

1. Homework Statement

A 12 g bullet passes horizontally through a 15 cm tall, 20 cm long .5 kg block which is initially at rest on a 1 meter tall table’s edge. The bullet is initially moving 230 m s , and it passes through the block. After the bullet passes through it, the block hits the ground 134 cm from the edge of the table.

## Homework Equations

**Δy = -4.9t**

K

^{2}K

_{f}=**K**

_{i}+ Wa) How fast is the block moving after the bullet emerges from it?

## The Attempt at a Solution

I solved this using projectile motion and got 2.97m/s:

Δy = -4.9t

^{2}

t

^{2}= -1/-4.9

t= 0.45s

v

_{x}= 1.34/0.45 = 2.97m/s

b) How fast is the bullet moving when it emerges from the block?

## The Attempt at a Solution

p of bullet initial = p of bullet final + p of block final

p of bullet initial - p of block final = p of bullet final

speed of bullet final = (p of bullet initial - p of block final)/(mass of bullet)

v = (0.012*230 - 2.97*0.5)/0.012 = 106m/s

c) Assuming that the block does not move significantly while the bullet is inside it, determine the average force exerted on the block by the bullet while the bullet passes through the block. Use energy!

## The Attempt at a Solution

Here is where I think I'm wrong:

K

_{block, final}- K

_{block, initial}= Fd

d = 0.2m because it goes through the length of the box.

so (K

_{block, final}- K

_{block, initial})/d = F

F = (0.5*0.5*2.97

^{2})/0.2 = 11N

My intuition tells me that 11N is SUPER low for a bullet flying through something. Maybe you would use 106m/s but I don't get why you would do that.