Question

Consider a 1 kg ball and a 6 kg ball of the same size dropped from a height of 3 m at the same time above the ground.

a) If we consider air resistance, do both objects fall or accelerate at the same rate? Explain.

b) If we dropped a 1 kg ball and a 1 kg square plate of dimension 20 cm x 20 cm, do both objects fall or accelerate at the same rate? Explain.

Answer 1

Air resistance on a falling object depends on it's area of cross-section. More the area more the value of air resistance is. Air resistance is always opposite to the motion of the object.

a). 1 kg and 6 kg balls have same size. That means, they have equal cross-sectional area. Same air resistance force will act on them. So, they will fall with same rate of the acceleration.

b). 1 kg square plate has larger cross sectional area. So, it counters the greater air resistance that makes it fall with the slower rate in compaeison to the 1 kg ball of smaller area. Therefore, both the objects fall with different accelerations.