Given mass, distance, and time, calculate power

[MathMajor]

Homework Statement

How much power does a weightlifter expend when lifting a 50kg barbell a distance of 1.2m in a time interval of 1.5s?

Homework Equations

Power=work done/time interval (in Newton meters per second or Watts)
Work=Fd (in Newton meters or Joules)

The Attempt at a Solution

Power = Fd/t = (m)(a)(d)/t = 50kg(9.8 m/s2)(1.2m)/1.5s = 392 Nm/s = 392 W

This is how I solved the problem, but my professor said the correct answer is 40 Watts!
Work = force x distance; work = 50 kg x 1.2 m, work = 60
Power = work /time; 60/1.5 = 40 Watt

Can someone please verify which way is correct? I am sticking by my answer of 392 Watts

 

[rock.freak667]

The Attempt at a Solution

Power = Fd/t = (m)(a)(d)/t = 50kg(9.8 m/s2)(1.2m)/1.5s = 392 Nm/s = 392 W

This is how I solved the problem, but my professor said the correct answer is 40 Watts!
Work = force x distance; work = 50 kg x 1.2 m, work = 60
Power = work /time; 60/1.5 = 40 Watt

'50kg' is a mass and not a force, it must be correctly multiplied by acceleration (gravity in this case) to convert it to a force. You are correct.

 

[MathMajor]

Ok, so you are sure the correct answer is 392 Watts? I feel like I will be shunned for going against the professor, but I have to go with my gut on this one.

Thanks!

 

[rock.freak667]

Ok, so you are sure the correct answer is 392 Watts? I feel like I will be shunned for going against the professor, but I have to go with my gut on this one.

Thanks!

I didn't check over your answer, but I am quite sure that 'kg' is a unit of mass and not force.

 

[MathMajor]

I agree. Thanks!