a mass m slides under the action of gravity inside a frictionless tube which is bent in the shape of a helix of radius a and pitch angle α. 34 kinematics: the description of motion the geometric axis of the helix is vertical. if the mass starts from rest at t = 0 from the point z-0 and φ = 0, find the er, e and ez components of the force exerted by the particle on the helix as a function of time

When a book falls from a shelf to the ground without anyone pushing on it, no work is done on the book. true or false

Under conditions for which the same room temperature is maintained by a heating or cooling system, it is not uncommon for a person to feel chilled in the winter but comfortable in the summer. provide a plausible explanation for this situation (with supporting calculations) by considering a room whose air temperature is maintained at 20â°c throughout the year, while the walls of the room are nominally at 27â°c and 14â°c in the summer and winter, respectively. the exposed surface of a person in the room may be assumed to be at a temperature of 32â°c throughout the year and to have an emissivity of 0.90. the coefficient associated with heat transfer by natural convection between the person and the room air is approximately 2 w/m2 â‹…â‹… k. what is the ratio of the thermal resistance due to convection to the thermal resistance due to radiation in the summer? what is the ratio of thermal resistances in the winter

Which example has gravitational potential energy? a. a horse slowing down from a run b. an apple about to fall from a tree branch c. a bicycle being pedaled down a horizontal path d. beaker sitting on the floor