# Two cars moving towards each other - bullets fired

#### Isobel

1. Homework Statement
This problem-solving question is about a police car chasing criminals.
Two cars are moving in the same direction, parallel (assumed).
One car is moving at 82 km/h.
The other car is moving at 64 km/h.
Bullets are fired from the car moving at 82 km/h towards the car moving at 64 km/h at a rate of 15 bullets per second.
a) what is the spread of the bullets that hit the car?
b) how many bullets hit the car?
2. Homework Equations
I think I'm supposed to use kinematic equations:
s=ut+0.5*at squared
v squared = u squared + 2as
v = u+at
s= (u+v)/2*t

3. The Attempt at a Solution
I got this question on an exam and I had no idea how to do it. This is just what I remember of the question.

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#### haruspex

Homework Helper
Gold Member
2018 Award
what is the spread of the bullets that hit the car?
Do you mean, at what rate do the bullets hit the other car?
What about the muzzle speed of the bullets, is that known?

#### kuruman

Homework Helper
Gold Member
You also need the length of the car to anwer (b).

#### gneill

Mentor
From the thread title it sounds like one car is behind the other, but from the problem statement it sounds more like the cars are side by side with one overtaking and passing the other. Assuming the latter the spread (or spacing) of the impacts can be found, but to answer (b) the length of the criminal's car would have to be known as observed by @kuruman.

I think we need to await the return of @Isobel for clarification.

#### CWatters

Homework Helper
Gold Member
I havent done the sums but it might be obvious how many bullets hit the car if the spread is large enough.

#### Isobel

From the thread title it sounds like one car is behind the other, but from the problem statement it sounds more like the cars are side by side with one overtaking and passing the other. Assuming the latter the spread (or spacing) of the impacts can be found, but to answer (b) the length of the criminal's car would have to be known as observed by @kuruman.

I think we need to await the return of @Isobel for clarification.
The cars are side by side with one overtaking the other.
The length of the criminal's car was not given, which is where I got stuck.
Perhaps you could assume the length of the car and work from there?

#### kuruman

Homework Helper
Gold Member
How about starting with part (a). I think by "spread" is meant the distance between successive bullets that hit the car. Can you find that? Think relative velocity.

"Two cars moving towards each other - bullets fired"

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