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Inertia
1. If an object remains at rest, there must be no force acting on it. Is this statement correct?
Explain.
(no, no net force)
2. If an object is moving with constant velocity (a) there must be a force in the direction of the
velocity, (b) there must be no force in the direction of the velocity, or (c) there must be no net
force.
(c)
3. An object weighs 300 N on Earth and 50 N on the Moon. Does the object also have less inertia
on the Moon?
(no, same mass, same inertia)
4. Consider an air-bubble level that is sitting on a horizontal surface (picture). Initially the air
bubble is in the middle of the horizontal glass tube. (a) If the level is pushed and a force is
applied to accelerate it, which way would the bubble move? Which way would the bubble move
if the force is then removed and the level slows down due to friction? (b)Ssuch a level is
sometimes used as an “accelerometer” to indicate the direction of the acceleration. Explain the
principle involved. [Hint: think about pushing a pan of water.]
(b) inertia of liquid)
5. Objects have no weight in outer space. How can you then distinguish their masses?
6. If your professor’s car is traveling west with a constant velocity of 55mi/h west on a straight
highway, what is the net force acting on it?
(zero)
7. A 5.0-kilogram block at rest on a frictionless surface is acted on by forces F1 = 5.5 N and F2 = 3.5
N, as illustrated. What in additional horizontal force will keep the block at rest? (F3 = (-7.6 N) x)