How much work (in j) must be done to lift a stack of bricks, which has a mass of 400 kg, from the ground to a height of 3 m? (g = 10 m/s2)?

Awoman stands a distance d from a loud motor that emits sound uniformly in all directions. the sound intensity at her position is an uncomfortable 2.0×10-3 w/m2. at a distance 2.6 times as far from the motor, what are (a) the sound intensity and (b) the sound intensity level relative to the threshold of hearing?

Work out sian speed for the first 30 minutes of her journey. give your answer in km/h.

Given the position vector of the particle r(t)=(t+1)i+(t^2−1)j+2t k, find the particle's velocity and acceleration vectors at t=1