How much work is a 200 kg weightlifter doing while he holds a 1000 kg barbell stationary .75 m over his head?
1000(.75)
= 7350 J
Stationary...no change in height is occuring.
To calculate the work done by the weightlifter, we can use the formula:
Work (W) = Force (F) * Distance (d) * cos(theta)
In this case, the weightlifter is holding the barbell stationary, so the net force acting on the barbell is zero. Therefore, the work done by the weightlifter is also zero.
The formula you used (Work = Force * Distance) assumes that the force and the displacement are in the same direction. However, in this scenario, the force exerted by the weightlifter is upward, while the displacement of the barbell is in the vertically downward direction. This means that the angle (theta) between the force and displacement is 180 degrees, and the cosine of 180 degrees is -1.
Using the correct formula, the work done would be:
Work (W) = Force (F) * Distance (d) * cos(theta)
= 1000 kg * 9.8 m/s^2 * 0.75 m * cos(180 degrees)
= -7350 J
So the work done by the weightlifter while holding the barbell stationary is -7350 Joules. The negative sign indicates that the work is being done against the force of gravity, which is pulling the barbell downwards.