Magnitude of Force?

A physical therapy exercise has a person shaking a 5.00 kg dumbbell up and down rapidly. If the barbell is moving at 4.50 m/s, what is the magnitude of the force required to stop it in 0.333 seconds?
Update: I think I may have the answer

f deltat= m deltav
F0.333=5.00x4.5
22.5/.333
F=67.6N
2 answers 2