An object is dropped from a height h. Apart from gravity, a drag force:

F = −kv

acts on the object. Choose the correct velocity-time graph.

Solution:

Equation of motion:

m dv/dt = mg − kv

Initially:

v = 0

As time increases:

• Velocity increases
• Acceleration decreases
• Velocity approaches terminal velocity

Therefore the graph:

• Starts from zero
• Rises rapidly
• Gradually becomes horizontal

This corresponds to Graph (2).

Answer: Option (2)