Physics

Problem

A worker lifts a uniform steel beam of mass

m

steadily from the ground to a height

h

in time

t

. a. (i) Derive an expression for the power required in terms of

m

g

h

and

t

when the beam is lifted at constant speed. b. (ii) Using your expression, calculate the power needed to raise a

40\,\text{kg}

beam through

3.0\,\text{m}

5.0\,\text{s}

. Take

g=9.8\,\text{m\,s}^{-2}

. c. (iii) If the actual lifting device is only

75\%

efficient, what should be the power rating of its motor to accomplish the same task in the stated time?