The diagram below shows the plan view of a door hinged at A. If a man applies a force, F, of 40 N at the end marked B, calculate the
moment of this force about A. What is the minimum force X that must
be applied at C in order to stop the door from turning? Name the
principle applied to solve this problem.
'1.8 m
B
A
1.2 m

Estimate the kinetic energy of mars with respect to the sun as the sum of two terms, that due to its daily rotation about its axis, and that due to its yearly revolution about the sun. (assume mars is a uniform sphere with mass = 6.4×10 to the power of 23 kg, radius = 3.4×10 to the power of 6 m, rotation period = 24.7 hours, orbital period = 686 days and is 2.3×10 to the power of 8 km from the sun.)