Why Does the Recoiling Cannon's Projectile Angle Calculation Seem Incorrect?

[Ara macao]

A circus cannon, which has a mass M = 4500 kg, is tilted at q = 30°. When it shoots a projectile at v0 = 60 m/s with respect to the cannon, the cannon recoils along a horizontal track at vcannon = 0.5 m/s with respect to the ground.

a) At what angle to the horizontal does the projectile move with respect to the ground?

I get tan $$\theta$$ = 60sin30 / (0.5+60cos30). But it's still wrong. Can someone tell me what I did wrong? Thanks

 

[daniel_i_l]

In this question the horizontal momentum is conserved, so you know that the final momentum of the cannon equals the final horizontal momentum of the projectile.
are you sure that you don't know the mass of the projectile? If you knew the mass then with that you could find the horizontal velocity and then the angle.