In my opinion, the correct answer among the choices listed above is option C. The Big Bang Theory states that between 15 and 20 billion years ago, the universe began expanding out of an enormous explosion. However, the exact number is approximately 13.8 billion years ago.
The big bang theory describes the beginning of the universe. According this theory, all the matter of the universe was confined at a point and about 15-20 billion years ago, it started expanding out of a huge explosion -the big bang. The universe has been expanding since then. The discovery of cosmic microwave background radiation provides the evidence to this theory.
If the maximum static frictional force is 90 N, this means that any applied force that will overcome this force, will cause the piano to slide, so kinetic frictional force applies.
Under these conditions, the net force in the horizontal direction is just the difference between the applied force (which is larger that the static friction force) and the kinetic frictional force, as follows:
By the same token, according Newton's 2nd Law, this force is just equal to the product of the mass of the piano, times the acceleration, as follows:
The first thing you should know is that the work is defined as: W = F * d Where F = force d = displacement We have then (a) the block F = (0.2) * (100) = 20 d = 100 W = (20) * (100) = 2000 ft.lbf (b) the man as the system. F = (0.2) * (100 + 180) = 56 d = 100 W = (56) * (100) = 5600 ft.lbf answer: (a) 2000 ft.lbf (b) 5600 ft.lbf
