Final answer:
The work done by a weight lifter holding a barbell stationary is 0 J because there is no displacement. To calculate power for lifting, work done is computed first and then divided by the time taken.
Step-by-step explanation:
In the case of a weight lifter holding a 150.0 N barbell stationary above his head, the work done is technically zero. This is because work (W) is defined in physics as the product of the force and the displacement in the direction of the force. Since the barbell is not moving (no displacement), the work done is W = force x displacement = 150.0 N x 0 m = 0 J (joules).
However, if we consider the question asking to estimate the power expended by a weightlifter raising a 150-kg barbell 2 m in 3 s, we use the formula P = W/t, where P is power, W is work done, and t is time. First, we calculate work: W = force x displacement = 150 kg x 9.8 m/s2 x 2 m. Then we divide the work by time to find the power. The gravitational acceleration (9.8 m/s2) is used to convert the mass of the barbell to weight (force), as weight is mass multiplied by gravitational acceleration.