How many neutrons does element X have if it's atomic number is 21 and it's mass number is 75

A heat engine produces 8200 j of heat while performing 3200 of useful work. what is the efficiency of this engine? (i'm doing something wrong.)

A car traveling at 54km/hr slows down uniformly to a velocity of 18km/hr when the break were gradually applied. 1. how long does it takes to cover a distance of 50m 2. what is the deceleration?

Whose assassination led to world war 1

Two eagles fly directly toward one another, the first at 15.0 m/s and the second at 21.0 m/s. both screech, the first one emitting a frequency of 2800 hz and the second one emitting a frequency of 3800 hz.

Ns:Select the correct answer. In a video game, a flying coconut moves at a constant velocity of 20 meters/second. The coconut hits an obstacle and moves in the opposite direction with a constant velocity of 10 meters/second.

What does law of conservation of mass mean?

Why do substances with free electrons make the best conductors.

Which of the following is evidence that groundwater causes erosion and deposition?

Which project involved the goal of orbiting a manned spacecraft around earth? A. Mercury B. Apollo C. Gemini D. Skylab

Which type of listening response includes the use of head nods, facial expressions, and short utterances such as "uh-huh" that signal your interest to the speaker?