equilibrium

A uniform plank with a length L of 6.10 m and a weight of 445 N, rests on the ground and against a frictionless roller at the top of the wall of height h = 3.05 m. The plank remains in equilibrium for any value of theta greater than or equal to 70 degress but slips if theta is less than 70 degrees. Find the coefficient of static friction between the plank and the ground.

Calculating the separation between two uniform spheres during gravitation.

From an inertial frame in space, we watch two identical uniform spheres fall toward one another owing to their mutual gravitational attraction. Approximate their initial speed as zero and take the initial gravitational potential energy of two-sphere system as Ui. When the separation between the two spheres is half the initial separation, what is the kinetic energy of each sphere?

Calculating the separation between two masses to attain a specified gravitational attraction.

What must the separtion be between a 5.2 kg particle and a 2.4 kg particle for their gravitational attraction to have a magnitude of 2.3 X 10(-12) N?

Gravitation

How far from Earth must a space probe be along a line toward the Sun so that the Sun's gravitational pull on the probe balances the Earth's pull?

Calculating the altitude above Earth's surface to attain a specified acceleration due to gravity.

At what altitude above the Earth's surface would the gravitational acceleration be 4.9 m/s^?