6.1. Universal Law of Gravity http://www.ck12.org
- Calculate the gravitational force that your pencil or pen pulls on you. Use the center of your chest as the center
of mass (and thus the mark for the distance measurement) and estimate all masses and distances.
a. If there were no other forces present, what would your acceleration be towards your pencil? Is this a
large or small acceleration?
b. Why, in fact, doesn’t your pencil accelerate towards you? - Mo and Jo have been traveling through the galaxy for eons when they arrive at the planet Remulak. Wanting
to measure the gravitational field strength of the planet they drop Mo’s lava lamp from the top deck of their
spacecraft, collecting the velocity-time data shown below.
TABLE6.1:
velocity (m/s) time (s)
0 0
3.4 1.0
7.0 2.0
9.8 3.0
14.0 4.0
17.1 5.0(a) Plot a velocity-time graph using the axes above. Put numbers, labels and units on your axes. Then draw a best-fit
line (use a ruler) and use that line to find the gravitational field strength of Remulak. Explain below how you did
that.
(b) Mo and Jo go exploring and drop a rock into a deep canyon –it hits the ground in 8.4 s. How deep is the canyon?
(c) If the rock has a mass of 25 g and makes a hole in the ground 1.3 cm deep, what force does the ground exert to
bring it to a stop?
(d) Mo and Jo observe the shadows of their lava lamps at different positions on the planet and determine (a la
Eratosthenes, the Greek astronomer, around 200 B.C.) that the radius of Remulak is 4500 km. Use that and your
result forgto find the mass of Remulak.