Force equals rate of change of momentum

Steps:

• Resultant force F = dp/dt, so momentum p changes at a rate equal to F.
• If F increases slowly with time, dp/dt increases gradually.
• Thus, the slope of the p-t graph starts small and becomes steeper over time.
• The graph must show p increasing with a concave-up curve.

Why B is correct:

• B depicts p rising with an increasing slope, consistent with F = dp/dt where F grows steadily.

Why the others are wrong:

• A shows constant p, implying zero force.
• C shows linear p increase, implying constant force.
• D shows decreasing slope, implying reducing force.

Final answer: B