What does the groupby() method do in the line: comp.groupby().shift(-1)

What condition is necessary to interpret Y ∼ X + e as “X causes Y”? 

Ramos CompanyRamos Company included the following information in its annual report:​201120102009Sales$178,400$162,500$155,500Cost of goods sold115,000102,500100,000Operating expenses50,00050,00045,000Net income13,40010,00010,500  Refer to the information for Ramos Company. In a common size income statement for 2011, the operating expenses are expressed as:

Which of the following are better indicated by percentage change statements than common-size statements?

Assets for a particular business might include:

To ensure that the financial statements articulate, it is important that the change in the cash balance on the balance sheet each year agrees with:

Preston pushes a wheelbarrow weighing 500 N to the top of a 50.0-m ramp, inclined at 20.0° with the horizontal, and leaves it. Tamara accidentally bumps the wheelbarrow. It slides back down the ramp, during which an 80.0-N frictional force acts on it over the 50.0 m. What is the wheelbarrow’s kinetic energy at the bottom at of the ramp? (g = 9.8 m/s2)

A 20-g bullet moving at 1 000 m/s is fired through a one-kg block of wood emerging at a speed of 100 m/s. What is the change in the kinetic energy of the bullet-block system as a result of the collision assuming the block is free to move?

A bucket of water with total mass 23 kg is attached to a rope, which in turn, is wound around a 0.050-m radius cylinder at the top of a well. A crank with a turning radius of 0.25 m is attached to the end of the cylinder. What minimum force directed perpendicular to the crank handle is required to just raise the bucket? (Assume the rope’s mass is negligible, that cylinder turns on frictionless bearings, and that g = 9.8 m/s2.)

A 50-N crate is pulled up a 5-m inclined plane by a worker at constant velocity. If the plane is inclined at an angle of 37° to the horizontal and there exists a constant frictional force of 10 N between the crate and the surface, what is the force applied by the worker?