Scientists suspect that Mars once had abundant liquid water on its surface. For this to have been true, early Mars must have had ________ than Mars today.

A) a much higher atmospheric pressure and much stronger greenhouse effect
B) a larger mass and radius
C) a smaller axis tilt and less elliptical orbit
D) larger polar caps and more dust storms


A) a much higher atmospheric pressure and much stronger greenhouse effect

Physics & Space Science

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Carnot Engine: A heat engine having the maximum possible efficiency has an efficiency of 35.0% when operating between two heat reservoirs. If the temperature of the hot reservoir is 700 K, what is the temperature of the cold reservoir?

A. 200 K B. 245 K C. 350 K D. 455 K E. 600 K

Physics & Space Science

Although the Sun does not generate energy by gravitational contraction today, this energy-generation mechanism was important when the Sun was forming

Indicate whether the statement is true or false

Physics & Space Science

A 6.0-kg object moving 5.0 m/s collides with and sticks to a 2.0-kg object. After the collision the composite object is moving 2.0 m/s in a direction opposite to the initial direction of motion of the 6.0-kg object. Determine the speed of the 2.0-kg object before the collision.

A. 15 m/s B. 7.0 m/s C. 8.0 m/s D. 23 m/s E. 11 m/s

Physics & Space Science

Amy, Brad, and Cate are walking (or running) along a straight line as represented below

Physics & Space Science