Problem 9. A) What is special about the center of mass of an object? B) Why don\
ID: 1458279 • Letter: P
Question
Problem 9. A) What is special about the center of mass of an object? B) Why don't internal forces change the velocity of the center of mass of a system of objects? C) A fully clothed person is in the middle of a large frictionless surface (perhaps a slippery lake or better a scientifically designed surface as large as a skating rink). The person is originally at rest. How might this person, by themselves, get off the surface? Explain! Problem 10. A) is more damage done in an elastic or inelastic collision between two cars? B) Build on the answer to part A) to explain why cars have bumpers? C) in terms of impulse and momentum, why are dashboards padded? D) in terms of impulse and momentum, why should golfers ''follow through on their swings''?Explanation / Answer
Pb 9:
A)
- the entire mass is concentrated in that small spot (which behaves like a small body having the total mass of the system, M).
- its position is independent of the distribution of the mass within the same frame/countour (for a homogenous body).
- for a homogenous body, its position depends on the geometrical properties of the body and not on the material.
- it's unique for a certain body.
- in a homogenous gravitational field, the center of mass=center of gravity.
B) The internal forces can only redistribute the mass of the system, and not changing CM because their resultant is 0.
C) By changing his/her position using his/her internal energy. (s)he's just redistributing his/her internal parts of the body.
Pb10:
A) In an inelastic collision heat is released. It of a high quantity, additional damage may occur (e.g., fire).
B) To avoid inelastic collision effects (e.g., the metal of the body can melt at high speed collision due to the high temperature, and "glue" the cars together, the shock of the impact).
C) To avoid transmiting the shock of the collision (and the heat resulted from it) to the passengers.
D) To compensate the shock of the hit/shot.
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