A 100-kg cannon at rest contains a 10-kg cannon ball.  When fired, the cannon ball leaves the cannon with a speed of 90 m/s.  What is the recoil speed of the cannon?​

Respuesta :

The recoil speed of the cannon is 9 m/s

Explanation:

We can solve the problem by using the law of conservation of momentum. In fact, the total momentum of the cannon+cannonball system before and after the shot must be conserved, in absence of external forces.

Before the shot, the total momentum is zero:

p = 0

After the shot, the total momentum is: given by:

[tex]p=mv+MV[/tex]

where :

m = 10 kg is the mass of the ball

v = 90 m/s is the velocity of the ball

M = 100 kg is the mass of the cannon

V is the recoil velocity of the cannon

Since momentum is conserved, we can write

[tex]0=p = mv+MV[/tex]

And solving for V, we find the recoil velocity of the cannon:

[tex]0=mv+MV\\V=-\frac{mv}{M}=-\frac{(10)(90)}{100}=-9 m/s[/tex]

And the negative sign means the cannon will move in the opposite direction to the cannonball: so, the recoil speed is 9 m/s.

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