- #1

songoku

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- Homework Statement
- A mass m is connected to a spring of spring constant k and performs simple harmonic motion with amplitude A on a horizontal surface. When the spring is stretched by A/2, another mass m falls vertically on first mass. What is the new amplitude of motion?

- Relevant Equations
- Simple harmonic motion

Conservation of momentum?

I am confused about conservation of momentum for this question.

I take the system as two objects, each having mass m. For first object (the one performing simple harmonic motion), there is net external force acting on it in horizontal direction (restoring force of spring). For second object (the one falling vertically), there is net external force acting on it (its weight).

1. The momentum in vertical direction is not conserved because initially (before they stuck), there is initial vertical momentum but after they stuck together, the vertical momentum is zero. But how about momentum in horizontal direction. I think momentum in horizontal direction is also not conserved because there is net external force in that direction. Or we can think it is also conserved because before and after they stuck there are net external force (and assuming these forces have equal magnitude)?

2. Do we need to consider momentum to solve this question?

Thanks

I take the system as two objects, each having mass m. For first object (the one performing simple harmonic motion), there is net external force acting on it in horizontal direction (restoring force of spring). For second object (the one falling vertically), there is net external force acting on it (its weight).

1. The momentum in vertical direction is not conserved because initially (before they stuck), there is initial vertical momentum but after they stuck together, the vertical momentum is zero. But how about momentum in horizontal direction. I think momentum in horizontal direction is also not conserved because there is net external force in that direction. Or we can think it is also conserved because before and after they stuck there are net external force (and assuming these forces have equal magnitude)?

2. Do we need to consider momentum to solve this question?

Thanks