Question

cynthia observes an object speed up when a force acts on it. if a constant force is causing the objects motion to change, which scenario might cynthia be observing?

a) a bat collides with a baseball; both fly off in opposite directions.

b) a raindrop forms in a cloud. it moves faster and faster as it falls to the ground.

c) two balloons are rubbed with fur; they push apart when brought near each other.

d) a compass is brought near one end of a magnet; the compass needle is pushed away.

Explanation:

Let's analyze each option:

• Option A: When a bat collides with a baseball, it is an impulsive force (not a constant force) that acts for a very short time.
• Option B: A raindrop falling to the ground is under the influence of gravity (a constant force, approximately \(F = mg\), where \(m\) is the mass of the raindrop and \(g\) is the acceleration due to gravity). As it falls, the force of gravity causes it to accelerate (speed up) as \(F=ma\) (\(a=\frac{F}{m}\), and if \(F = mg\), then \(a = g\) in the absence of significant air - resistance in the initial stages of fall).
• Option C: The force between two charged balloons (after being rubbed with fur) is an electrostatic force. Electrostatic force \(F=\frac{kq_1q_2}{r^{2}}\), where \(k\) is a constant, \(q_1\) and \(q_2\) are the charges on the balloons, and \(r\) is the distance between them. As the balloons move apart (\(r\) increases), the force \(F\) decreases. So, it is not a constant force.
• Option D: The force between a compass needle and a magnet is a magnetic force. Magnetic force \(F = BIL\sin\theta\) (for a current - carrying wire, but for a compass needle, the force is more complex in terms of dipole - dipole interactions). As the compass needle moves, the strength and direction of the magnetic force change depending on the orientation and distance from the magnet. So, it is not a constant force.

Answer:

B. A raindrop forms in a cloud. It moves faster and faster as it falls to the ground.