Question

A bullet of mass 15g has a speed of 400m/s . what is its kinetic energy? if bullet strikes a thick target and is brought to rest in 2 cm , calculate the average net force acting on the bullet ?

Answer 1

Answer:

1,200 J and 60,000 N

Explanation:

m = 15g = 15/1000 kg

u = 400 m/s

i) K.E. = 1/2 mu^2

= 1/2 * 15/1000 * 400 * 400

= 1/2 * 15 * 40 * 4

= 15 * 80

= 1200 J

ii) Now, V = 0 m/s

S = 2 cm = 2/100 m

Now, using the third equation of uniformly accelerated motion,

V^2 - u^2 = 2aS

0 - 400 * 400/ 2 * 2/100 = a

So

a = - 400 * 400 * 100/2 * 2

a = - 100 * 100 * 400

a = 4,000,000 m/s^2 (4 * 10^6 ms^-2)

Now, by Newton's Second Law of Motion,

F = ma

F = 15/1000 * 4,000,000

F = 15 * 4,000

F = 60,000 N (6 * 10^4 N)