Question

A student is testing the kinematic equations for uniformly accelerated motion by measuring the time it takes for light-weight plastic balls to fall to the floor from a height of 3 m in the lab. The student predicts the time to fall using g as 9.80 m/s2 but finds the measured time to be 35% greater. Which of the following is the most likely cause of the large percent error?
(A) The acceleration due to gravity is 70% greater than 9.80 m/s2 at this location.(B) The acceleration due to gravity is 70% less than 9.80 m/s2 at this location.(C) Air resistance increases the downward acceleration.(D) The acceleration of the plastic balls is not uniform.(E) The plastic balls are not truly spherical.

Answer 1

Answer: Conclusion E

Explanation:

In this study we need to keep several things is mind.

First, the atracttion between two objects can be calculated using Newton's Universal Gravitation Equation:

$F = G * \frac{M_{1} * M_{2}}{r^{2} }$

Where the Force of attraction between two objects can be calculate by the product of the Gravitational Constant (G), their masses between the square of the distance. This same equation can be used to obtain the acceleration caused by gravity.

If we take in account this equation, we know that the Earth Mass is so big that any other will be attracted using the same force, no matter his size. Because of this, while the attraction between a Plastic Ball and a Rock should be different, the Earth's Mass makes irrelevant any weight like a little fluctuation.

Because of this, the Acceleration due Gravity should be constant between any object. A 70% bias is imposible. This made conclusions A, B and D Falses.

However the previous equation doesn't take in count the medium on which the two objects move. It is know that a object moving inside a fluid will experience friction which a force that oposses movemente and goes on the contrary direction, While the Plastic ball falls, the air around it will cause friction. This friction will always slow a falling object. Proving then, Conclusion C is false

In the case that a object falls, the air can provide resistant as proved before, however any irregularity on the surface of the ball can cause the ball to move and making the fall not truly straight, this can increase the time travel of the ball and slowing the ball fall. For this Conclusion E is the most likely to cause the error