Recent content by BlackJ

Homework Statement [/B] (1)A sphere of radius 0.500 m, temperature 27.0 C, and emissivity 0.850 is located in an environment of temperature 77.0 C. At what rate does the sphere (a) emit and (b) absorb thermal radiation? (c) What is the sphere’s net rate of energy exchange? (2)A cylindrical...

Argh I kept thinking -Wg already included the negative sign so I substitute mgh instead of -mgh It's just clear now, thanks a lot.

does that mean g= -9.8m/s^2 instead of 9.8 because gravity applied a force in opposite direction of force a?

Sorry I thought you ask what Wg is. I understand why the net work done on the box is zero, just still confused how the right answer is in positive but not negative after solving the equation Wa+Wg=0 As I see here Wa+Wg= 0 => Wa= -Wg= -mgh Isn't the answer in negative?

Isn't it the work from gravity force?

Homework Statement A constant force (Fa) of magnitude 82.0 N is applied to a 3.00 kg shoe box at an angle of 53.0 degrees, causing the box to move up a frictionless ramp at a constant speed. How much work is done on the box by Fa when the box has moved through a vertical distance h = 0.150 m...