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Aug 09

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Can you find the impracticability of the following question?

The following question is from a recent question paper for class XI Physics where the teacher tried to restructure a question from NCERT Textbook in Physics for Class XI. This is an example where careless restructuring creates problematic situation. However, can you tell me what is the impracticability with  the following problem? Also tell me what assumptions can make the question right.

Q. A police van moving with a speed of 36 km/h fires a bullet at a thief’s  car  speeding away in the same direction with a speed of 180 km /h  . If the muzzle speed of bullet is 150 m/s , what is the time taken by the bullet to hit the thief’s car, if the distance between the two vehicles is 1km at the instant the bullet is fired.In a position time graph represent the motion of the police van ,  thief’s car and the bullet.

 [The unmodified question from textbook is given below, which is harmless]

A police van moving on a highway with a speed of 30 km/h fires a bullet at a thief’s car speeding away in the same direction with a speed of 192 km/h. If the muzzle speed of the bullet is 150 m/s, with what speed does the bullet hit the thief’s car ? (Note: Obtain that speed which is relevant for damaging the thief’s car).


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