A bullet of mass 50g is fired from a rifle with a velocity of 300m/s. It hits a bank of earth and after travelling 60cm into the bank comes to rest. What is the average stopping force of the earth in the bank on the bullet?

Answer:

15) B

Equation for Force is: Force = mass x acceleration
We know the mass is 50g which is equal to 0.05kg

To find the acceleration we need to use the XUVAT or SUVAT equations:

• v² – u² = 2as
• v = u + at
• s = ut + 1/2 at²
• s = 1/2 (u + v) t

We have the following information: 
v = 300m/s, 
u = 0 m/s,
s = 60cm = 0.6m, t = not known (cannot use eq 2, 3 and 4) 
a = value we want to find out. 

Therefore, we will have to use the first equation, v² – u² = 2as.

300² – 0² = 2 x a x 0.6
9000/1.2 = a
a = 7500 m/s

Force = 0.05 x 7500 = 3750 N = 3.75 x 10³ N