# Physics

Problem 1.

Homework Assignment 3

1. A)  Find your weight (near the surface of the earth) in Newtons.
2. B)  Find your mass in kilograms.
3. C)  Find what your weight in Newtons would be if you were in an orbit at a distance of 2 earth radii above the surface of the earth. (So you would be three earth radii from the center of the earth.)

Problem 2.

1. A)  Use the gravitational force law to nd your weight on the surface of Venus. (Look up the mass and radius of Venus on the web or elsewhere.)
2. B)  Calculate (don’t just look up) the gravitational eld strength gV (acceleration due to gravity) on the surface of Venus.

Problem 3.

1. A)  Compare (by doing the calculations) the gravitational force that the earth exerts on the moon to the gravitational force that the sun exerts on the moon. (Look up needed physical data on the web.)
2. B)  In part A) you should have found that the force that the sun exerts on the moon is larger than the force that the earth exerts on the moon. Why, then, doesn’t the sun pull the moon away from the earth?

Problem 4.

1. A)  Is the gravitational force that the earth exerts on a falling eraser greater than, equal to, or less than the gravitational force that the falling eraser exerts on the earth. Briey justify your answer.
2. B)  Why does the falling eraser of part A) accelerate towards the earth more than the earth accelerates towards the eraser?

Problem 5. Indicate whether each of the following statements is true or false. Briey justify your answers. A) An object that has zero velocity, at a given instant, must be experiencing zero net force at that instant. B) An object has the same mass when on earth and when on the moon.
C) An object has the same weight when on earth and when on the moon.

D) The gravitational force between two protons is greater in size than the electrostatic force between the two protons.

Problem 6. Consider a ball thrown straight up in the air which then returns to the level from which it was thrown. Noting that the acceleration of the ball is in the direction of the change in velocity of the ball, determine the direction of the acceleration of the ball

A) at a point on the upward path of the ball.
B) at the very top of the ight.
C) at a point on the downward ight of the ball.

Extra Credit: (5 pts) According to Newton’s Second Law, more massive objects tend to be harder to accelerate. Why then

do all objects, regardless of mass accelerate at the same rate when in free fall?

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