Question

A bullet of mass m=200g travelling horizontally with a velocity of v=100m/s penetrates sand bag up to 50cm and stops. The average resistance force exerted on the bullet by sand in the bag in kN is

Answer 1

Given :

mass of the bullet, m = 200 g = 0.2 Kg

Initial Velocity, u = 100m/s

distance covered, s = 50 cm = 0.5m

final velocity, v = 0m/s

To find :

The average resistance force exerted on the bullet by sand in the bag

Solution :

first of all we have to find accerlation

as we are provided with initial Velocity, distance and final velocity we can use 3rd equation of motion .i.e.,

➠ v² - u² = 2as

➠ (0)² - (100)² = (2)(a)(0.5)

➠ a = -10000/1

➠ a = -10000

Remember !

if the speed is decreasing with time then accerlation is negative and it is called retardation.

Now, using second law of motion .i.e.,

$\bigstar$The rate of change of linear Momentum of a body with time is proportional to the net external force acting on it.

In order words,

• F = ma

here,

F denotes force

m denotes Mass

a denotes accerlation

by substituting all the given values in the formula,

➠ F = ma

➠ F = (0.2)(10000)

➠ F = 2000N

➠ F = 2kN

thus, The average resistance force exerted on the bullet by sand in the bag is 2kN.

Remember !

SI unit of force is Newton (N).