Homework Help: Concept MC Questions

1. Dec 7, 2005

bobby13

Hi, I have some review multiple choice questions, and some of them, I cant understand why the answer is so. If you could clarify the concepts, that'd be great!

Which statement best describes the Earth’s rotation about its
axis?
a)The tangential velocity is the same at all points on the Earth’s
surface.
b)The angular velocity is greatest at the Earth’s equator.
c)The angular acceleration is zero at all points on the Earth’s
surface.
d)The centripetal acceleration of a point on the Earth’s surface
is zero.

The answer is C. For this one, I didnt even know where to begin. I only could eliminate D because since it is rotating, it has to have a centripetal acceleration.

A ladder leans against a frictionless wall, but is prevented from
falling because of friction between it and the ground. If you
shift the base of the ladder toward the wall,
a) The normal force on the ladder from the ground decreases.
b) The static frictional force on the ladder from the ground
decreases.
c) The normal force on the ladder from the wall increases.
d) The maximum static frictional force on the ladder from the
ground increases.
e) None of the above.

The answer is B. I thought the answer was E because the normal force is the same, and the cofficient of static friction is the same, then the force of static friction should be the same.

Two astronauts (both 70 kg) are floating motionless in empty
space far from the Earth. One of them is holding a 20-kg
oxygen tank. He pushes the tank directly toward the second
astronaut, who catches and holds it. If the speed of the tank
relative to the second astronaut was 2.0 m/sec, then the final
speed of the second astronaut relative to the first one (after the
second one has caught the tank) is:
(A) 0.4 m/sec
(B) 0.6 m/s
(C) 1.0 m/s
(D) 1.5 m/s

Answer is C. Im really not too sure where to being here