How many teeth does an average human have

The scientific principle which explains the observation that the amount of heat transfer accompanying a change in one direction is numerically equal but opposite in sign to the amount of heat transfer in the opposite direction is:

An open train car, with a mass of 2150 kg, coasts along a horizontal track at the speed 2.83 m/s. The car passes under a loading chute and, as it does so, gravel falls vertically into it for 2.95 s at the rate of 481 kg/s.

Why is the true surface of a perfect mirror invisible?

Allison (of mass 20 kg) is coasting in her wagon (of mass 20 kg) at a constant velocity of 7 m/s. She passes her mother, who drops a bag of toys (of mass 2 kg) into the wagon. What will happen to the speed of the wagon?

What is electromagnetic wave made of

When distances were carefully measured from Earth to globular clusters above and below the Milky Way plane (where our view of them is not obscured by interstellar dust and gas), their distribution was found to be

Imagine you transfer heat into a gas. This heat splits up in two different ways: Additional thermal energy making the gas hotter and "fuel" for the gas to do work. Let's suppose, 64% of the transferred heat transforms into thermal energy.

How much heat is absorbed by a 61g iron skillet when its temperature rises from 5oC to 29oC?

Explain the relationship between motion and frame of reference.

Two students are looking at a brightly lit full Moon, illuminated by the reflected light from the Sun. Consider thefollowing discussion between the two students about what the spectrum of moonlight would look like.