# A firing marksman

1. Oct 15, 2006

### mikefitz

These problems with x and y components always leave me confused....

A marksman standing on a motionless railroad car fires a gun into the air at an angle of 30° from the horizontal (the figure below ). The bullet has a speed of 173 m/s (relative to the ground) and a mass of 0.02 kg. The man and car move to the left at a speed of 1.2 " × 10-3 m/s after he shoots. What is the mass of the man and car? [Hint A component of a system's momentum along an axis is conserved if the net external force acting on the system has no component along that axis.]

http://img248.imageshack.us/img248/1495/fig026vo8.gif [Broken]

I know that momentum is conserved in the form of Pi = Pf. What I don't know is how to calculate the momentums when there are angles involved... Can someone help me get started on this problem please? Thanks

Last edited by a moderator: May 2, 2017
2. Oct 15, 2006

### OlderDan

Before the bullet is fired, the total momentum is zero. After the bullet is fired, the horizontal momentum is zero. The bullet also has vertical momentum, but the car cannot move downward to cancel the vertical bullet momentum, so the total vertical momentum after firing is not zero. All you need to find the solution is to work out the horizontal problem.