Forces and Motion?

Question

1) How does an object's speed affect aerodynamics? How can these aerodynamics be optimized?

2) As a rock accelerates upwards, its thrust remains constant, but its acceleration increases. What is the cause of this acceleration?

3) The force of gravity on a 2.0kg rock is twice as great as than a 1kg rock. Why then doesn't the heavier rock fall faster?

4) Explain a situation when the normal force is not equal to the force of gravity.

5) A stone is launched upward into the air. In addition to the force of gravity, the stone is subject to frictional forces due to air resistance. Is the time to reach the top of its flight equal to, smaller, or larger than the time to come back to its original position?

Answer 1

1.  Aerodynamic drag increases with increasing speed.  Aerodynamic drag generally acts opposite direction of motion.  You also have induced drag or drag due to lift.  Optimization really depends on what you are optimizing (fuel, speed, heat, etc)

2.  Acceleration increases vertically because the acceleration due to gravity decreases the further you move away from the gravity source.  I.e.- gravity is weaker on a mountain top than it's base.

3.  Force equals mass times acceleration.  With twice the mass and twice the force, acceleration is constant.

4.  Normal force could be greater than gravity if you apply additional force on top of it.  i.e.-if there is a block at rest with 1N gravity force, but I am pushing down on it with spring, etc then the normal force will be greater.  Could also apply if there are magnets, or if there is a rope with tension taking some of the load away from normal force.

5.  Same.  Air resistance will be based on speed and time at speed.  Since the only acting force is gravity, the rock will follow a ballistic path where upward route is mirror of downward.