a bullet moving at speed of 400m/s just pierous wooden blocks 4 cm thick what speed required to just fear about 9 cm
Answers
A bullet moving at a speed of 400m/s just pierces a wooden block 4 cm thick. To find : The speed that will be required to just pierce a wooden block 9 cm thick.
We know that, u^2 = v^2 - 2as
where u = Initial velocity
v = Final velocity
a = Acceleration
s = Distance
Let us consider that the moment the bullet hits the brick be initial velocity.
And the moment the bullet just pierces the brick be final velocity which will be equal to zero as the bullet stops in that portion.
And the distance covered be 's' due to deceleration 'a'.
And convert all the values to a same unit. So first distance covered, s = 0.04m and second distance covered, s= 0.09m.
So, putting the values we get,
(400)^2 = (0)^2 - 2 x (a) x (0.04)
Calculating the above equation we get, a = - 2 x 10^6 m/s^2.
Here we see that we got the value of a as negative which means that there is deceleration of bullet inside the wooden block.
So, speed required to just pierce a wooden block of 0.09m will be :
u^2 = (0)^2 - 2 x (-2 x 10^6) x (0.09)
Calculating the equation we get, u = 600 m/s.
Hence the Initial Velocity required to just pierce through a wooden block of 9cm will be 600m/s.