Question:

A police van moving on a highway with a speed of $ 30\, km\, h^{-1} $ fires a bullet at a thief?s car speeding away in the same direction with a speed of $ 192\, km\, h^{-1} $ . If the muzzle speed of the bullet is $ 150 \,m \,s^{-1} $ , with what speed does the bullet hit the thief?s car ?

Updated On: Jul 5, 2022
  • $ 95 \,m \,s^{-1} $
  • $ 105 \,m \,s^{-1} $
  • $ 115 \,m \,s^{-1} $
  • $ 125 \,m \,s^{-1} $
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The Correct Option is B

Solution and Explanation

Speed of police van w.r.t. ground $ \therefore v_{PG}=30\,km\,h^{-1} $ Speed of thief?s car w.r.t. ground $ \therefore v_{TG}=192\,km\,h^{-1} $ Speed of bullet w.r.t. police van $ v_{BP}=150\,ms^{-1}=150\times\frac{18}{5}km\,h^{-1}=540\,km\,h^{-1} $ Speed with which the bullet will hit the thief?s car will be $ v_{BT}=v_{BG}+v_{GT}=v_{BP}+v_{PG}+v_{GT} $ $ =540\,km\,h^{-1}+30\,km\,h^{-1}-192\,km\,h^{-1} $ $ \left(\because v_{GT}=-v_{TG}\right) $ $ =378\,km\,h^{-1}=378\times\frac{5}{18}\,ms^{-1}=105\,ms^{-1} $
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Concepts Used:

Motion in a straight line

The motion in a straight line is an object changes its position with respect to its surroundings with time, then it is called in motion. It is a change in the position of an object over time. It is nothing but linear motion. 

Types of Linear Motion:

Linear motion is also known as the Rectilinear Motion which are of two types:

  1. Uniform linear motion with constant velocity or zero acceleration: If a body travels in a straight line by covering an equal amount of distance in an equal interval of time then it is said to have uniform motion.
  2. Non-Uniform linear motion with variable velocity or non-zero acceleration: Not like the uniform acceleration, the body is said to have a non-uniform motion when the velocity of a body changes by unequal amounts in equal intervals of time. The rate of change of its velocity changes at different points of time during its movement.