
2-1 (f) Momentum and a variable mass
Point 6 of 7 — Motion with Variable Acceleration and ForceQuestion bank: 0 questions (0 with pictures)
06 2-1 (f) Momentum and a variable mass
Rules
- The momentum is and the force is .
- If the velocity is constant and the mass changes, .
- If the mass is constant, .
- A constant rate of gain or loss gives .
✍️ Worked examples
Example 16: A body of mass kg moves with velocity m/s along a line. Find the momentum and the force at .
Solution:
- .
- ; at , N.
- Check by the product rule: N.
Example 17:
- A metal ball of mass 100 g moves at constant 10 m/s through dusty air; dust sticks to it at 0.6 g/s.
- Find its mass and the force on it at time .
Solution:
- Mass: g.
- Force: dyne, constant.
Example 18: The displacement of a body of variable mass g is cm. Find the momentum and the force at .
Solution:
- ; g·cm/s.
- ; at , dyne.
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