(a) What do you mean by rest?​

Apassenger walks toward the rear of a moving train. describe her motion as seen from a reference point on the train. then describe it from a reference point on the ground

An engineer designs a roller coaster so that a car travels horizontally for 162 ft, then climbs 127 ft at an angle of 31.0° above the horizontal. it then moves 127 ft at an angle of 46.0° below the horizontal. if we take the initial horizontal motion of the car to be along the +x-axis, what is the car's displacement? (give the magnitude of your answer, in ft, to at least four significant figures and give the direction of your answer in degrees counterclockwise from the +x-axis.)

How can waves travel through ground?