Physics homework question. Real answers only?

Question

A bullet travelling horizontally at a speed of 350 m/s hits a board perpendicular to the surface, passes through it, and emerges on the other side at a speed of 210 m/s. If the board is 4.00 cm thick, how long does the bullet take to pass through it?
I also need an idea how it is worked.

Answer 1

0.000143 seconds, 0,143 milliseconds, or 143 microseconds, whichever you prefer.

In this problem, we can ignore gravity. We assume the bullet goes straight through horizontally. What's happening is that the board slows down the bullet (deceleration or negative acceleration). We'll also assume (because we don't know otherwise) that the deceleration is linear.

Under these circumstances, the through the board is (350 + 210)/2 = 280 m/s = 28000 cm/s.

Velocity is distance divided by time, so the time it took for the bullet to pass through is 4 cm / 28000 cm/s = 0.000143 seconds, which is the same as 0.143 milliseconds (ms) or 143 microseconds (mu s), whichever you prefer.

Answer 2

Basically, as the bullet passed through the target, it went from 350 m/s to 210 m/s, which is deceleration. What you have is an initial velocity = 350 m/s and a final velocity = 210 m/s

The distance over which it decelerated is 4.00 cm, or .04 meters.

The equation needed relates v0, vf, a and d.


Try: vf^2 = v0^2 + 2*a*d

(210)^2 = (350)^2 + 2*a*.04
a = -980,000 m/s^2

With "a" now known, find "t"

se:
vf = v0 + a*t


210 = 350 + (-980,000)*t
-140 = (-980,000)*t
t = 0.00014 seconds

Answer 3

First assume that the bullet slows down at a uniform rate as it is passing through the board.
To solve this use the equation: xfin=xin + vin*T +1/2 A*T^2
Lets let xinitial equal zero (right when the bullet first makes contact with the board). Therefore, xf=vin*T+1/2*A*T^2.
Lets also use the fact that A*T is the amount of velocity that the bullet lost during the trip through the board: -140.
Okay, xfinal is .04m--the distance the bullet travels through the board. And vinitial equals 350 m/s.
Therefore, 4=350*T+.5*(-140)*T
.04=T*(350-70)
.04=280T
T=.04/280
T=1.42x10^(-4)seconds

Answer 4

Find the average speed of the bullet in the wood. That's the average of 350 and 210. Next, find out how long it takes at that speed to travel 4 cm. Remember to convert the veleocity in m/s to cm/s by multiplying by 100.

Answer 5

acceleration ( or deceleration) is delta v/delta t

and x = 1/2 at^2+vot +xo if you don't recognize this the problem's going to be really tough! vo is initial v and xo is initial x
vo=350
xo=0

You want to know delta t (which we'll just call t) at x=4
vfinal=at+vo so you can substitute for a (or t) and solve.

Answer 6

average speed = (350+210)/2 =280 m/s
time = distance/speed = 0.04/280 =1.43E-4 s

Answer 7

I'm forgetting this stuff but here's a hint





Distance=(Rate)(Time)