Question

An iron cannon ball and a bowling ball are dropped at the same time from the top of a building. At the instant before the balls hit the sidewalk, the heavier cannonball has a greater?A. velocity. B. aceleration. C. kinetic energy. D. all of these are the same for the two balls.

Answer 1

Answer:

C. kinetic energy

Explanation:

Free Fall

When objects are dropped in free air (no friction), they are attracted to the Earth's surface by the force of gravity. Objects start from zero speed and gradually increase it because of the effect of the acceleration of gravity whose value can be considered as constant $g=9.8\ m/s^2.$

The final speed of the object at time t is

$v_f=g.t$

Note that the final speed does not depend on the mass of the object. The kinetic energy is

$\displaystyle k=\frac{mv_f^2}{2}$

The kinetic energy depends on the speed and the mass, so heavier objects dropped from the same height will have more kinetic energy. Let's analyze the options given in the question .

A. As shown above, the speed (or magnitude of the velocity) is the same regardless of the object's mass, so the heavier cannonball and the iron cannon will reach the ground at the same speed. Incorrect option

B. For every falling object in free air, the only acceleration is the acceleration of gravity. This option is not correct either

C. The kinetic energy is greater for the heavier cannonball because it has more mass, as discussed above. Correct option

D. Only the C. option is correct. This is not