Motion of a Charged Particle in Magnetic Field

[Ignitia]

Homework Statement

Viewers of Star Trek have heard of an antimatter drive on the Starship Enterprise. One possibility for such a futuristic energy source is to store antimatter charged particles in a vacuum chamber, circulating in a magnetic field, and then extract them as needed. Antimatter annihilates normal matter, producing pure energy. What strength magnetic field is needed to hold antiprotons, moving at 5.0×107m/s in a circular path 2.00 m in radius? Antiprotons have the same mass as protons but the opposite (negative) charge.

Homework Equations

F = ma = m * (v²/r)
F = qvB

The Attempt at a Solution

Okay, this is pretty straightforward:

v = 5.0x10^-7 m/s
m = 1.672x10^-27 kg
q = -1.6x10^-19C
r = 2m

F = qvB
F/(qv) = B
[(m*(v²) / r ] * 1/(qv) = B
(mv/rq) = B

Plugging in the values, answer becomes - 0.26T, but the correct answer is 0.26T. What am I missing?

 

[kuruman]

Strength of magnetic field is another name for magnitude which is a positive number.

 

[Ignitia]

Strength of magnetic field is another name for magnitude which is a positive number.

So I just take the absolute value? That makes sense, thanks.