# ncert-qn-3.18 motion in one dimension

3.18 A police van moving on a highway with a speed of
30 km hâ€“1 fires a bullet at a thiefâ€™s car speeding away
in the same direction with a speed of 192 km hâ€“1. If
the muzzle speed of the bullet is 150 m sâ€“1, with
what speed does the bullet hit the thiefâ€™s car ? (Note:
Obtain that speed which is relevant for damaging
the thiefâ€™s car).

the answer will be the relative velocity of the bullet wrt the thief's car rite ? if its so, then will it not depend on distance or anything ? bcoz it may b so the the thief is far away. pls explain me.

1
varun ·

speed of the police relative to the theif = 162 km/h

Now speed of bullet = 150m/s = 540 km/hr.

Relative speed of bullet and theif vehicle = 378 km/h.

62
Lokesh Verma ·

the answer will be the relative velocity of the bullet wrt the thief's car rite ? if its so, then will it not depend on distance or anything ? bcoz it may b so the the thief is far away. pls explain me.

Will paromita.. you are right.. in real life what will happen is that when u are very far the thing which is thrown at you might slow down.. (Bcos of things like air resistance etc)

here what will happen is that the bullet does not slow down.. it just keeps moving with the same velocity. So does the thief's car..

Thus they will meet after sometime. bcos the bullet is travelling faster... and the interesting thing is that they will meet even with the same speed as they initially had!