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Make a model to describe the path a bullet takes after being fired from a gun 3.5 m from the ground traveling?
Make a model to describe the path a bullet takes
after being fired from a gun 3.5 m from the ground
traveling 400 m/s and hitting the ground 2,200 m
from where it was shot (assuming a constant
deceleration). How far would it travel in 4
seconds
2 Answers
- 10 years agoFavorite Answer
[The bullet is fired 'mostly' upwards into the air from the numbers given]
Important point is assuming constant deceleration so we can use the "suvat" equations.
Note here I use vectors. If you're unfamiliar with them, basically a vector ( A , B )' just means A horizontally (x direction) and B vertically (y direction) and we usually assume that 'right' and 'up' are the positive directions, like a graph.
s = displacement at time t = ? m
u = initial velocity at time 0 = 400 m/s in an unknown direction = (400cosA, 400sinA)
v = velocity at time t = ? m/s
a = constant acceleration = (0, -g)' m/s
t = time = 4 s
initial displacement = (0, 3.5)' m
final displacement = (2200, 0)' m
total time = T = ? s
where g = acceleration due to gravity, approx 9.81 m/s^(2)
and A is the angle (between 0 and 90 degrees) made between initial direction and horizontal.
and we pick from a choice of common equations the one(s) to get what we want:
v=u+at
s=(1/2)(u+v)t
s=ut+(1/2)at^2
v^2=u^2+2as
a=(v-u)/t
Consider the total journey of the bullet first, so at time T.
s=ut+(1/2)at^2 taken horizontally gives
2200 = 400cosAT + (1/2)*0*T^2 = 400cosAT
T = (11/2cosA)
s=ut+(1/2)at^2 taken vertically gives
-3.5 = (1/2)(-9.81)T^2
T = sqrt(3.5*2/9.81) = 0.84472338...
so cosA = 0.84472338... *2/11 = 0.1535860...
and A = arccos(0.1535860...) = 81.165197... degrees
So now consider the system at 4 seconds
s=ut+(1/2)at^2 taken horizontally gives
s = 4*400cosA + 0.5*16*0 = 1600cos(81.165197...) = 1600*0.1535860... = 245.73771... m
s=ut+(1/2)at^2 taken vertically gives
s = 4*400sinA + 0.5*16*(-9.81) = 1600sin(81.165197...)+ 8*(-9.81) = 1 502.5364... m
so distance travelled is sqrt(245.73771...^2 + 1 502.5364...^2) = 1 522.4988... m
= 1522.50 m approx
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