1. What does it mean for a physical quantity to be...

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What does it mean for a quantity to be conserved? Why are conserved physical quantities useful to physicists? Give an example which illustrates the difference between three kinds of energy and the transformation of energy from one kind to another. Your example may include some of the following kinetic, thermal, gravitational potential, and spring potential energy. In your example explain the difference between Energy, Work, and Power.

Madhur L.

1. Under what conditions is the total momentum conserved in a collision? Under what conditions is the total energy conserved? The total kinetic energy? 2. Why are cars designed so that their front ends crumple during an accident? 3. You are standing perfectly still and then take a step forward. Before the step, your total momentum was zero, but afterwards you have some momentum. Does this violate conservation of momentum? Explain. 4. In numerous action movies the bad guy is shot with a bullet from a handgun and goes flying backwards due to the impact. Is this realistic? Explain why or why not. 5. A sharpshooter fires a rifle while standing with the butt of the rifle against her shoulder. If the forward momentum of the bullet is the same as the backward momentum of the gun, why isn’t it as dangerous to be hit by the gun as by the bullet? 6. Explain how a rocket can fly through space. 7. What do we mean by reference frame? 8. What quantities are conserved when a heavy nucleus undergoes fission and splits up into lighter ones? List as many as you can (there are lots). 9. You are designing a nuclear reactor and know that you need to work out a way to slow down neutrons to mediate the nuclear reactions. Should you use a material that is made up of heavy atoms, like lead, or lighter atoms, like carbon? Explain your decision.

Timothy J.

16-theory-questions-1-1-pt-if-a-quantity-called-a-is-conserved-what-is-its-derivative-a-2-1-pt-you-are-in-a-stationary-sailboat-in-a-still-body-of-water-on-a-windless-day-on-the-boat-you-fin-96777

1.6 Theory Questions 1. (1 pt) If a quantity called A is conserved, what is its derivative dA/dt? 2. (1 pt) You are in a stationary sailboat in a still body of water on a windless day. On the boat, you find a large, powerful fan. What is the most effective way to orient the sail and fan to propel the boat forward? Is is even possible use the fan to move the boat? 3. (1 pt) The moon has no atmosphere, so objects are free to move above the surface without any effects from nonconservative forces. An astronaut finds an ideal trampoline that dissipates no energy and fixes it to the ground to perform an experiment. First, she drops a marble onto the trampoline and measures the maximum height reached after one bounce. Then, she repeats the experiment using a bowling ball dropped from the same height. Does one object bounce higher than the other? Explain. 4. (1 pt) A rocket generates thrust by ejecting particles from its exhaust. During lift-off, the exhaust pushes directly against the surface of the earth. If the rocket is floating in the vacuum of space, far away from any surfaces, can the same engine be used for propulsion? 5. (1 pt) Use the definitions of momentum p₁ = m₁v₁ and kinetic energy K = 1/2m|v|² to express the kinetic energy in terms of momentum. 6. (1 pts) This problem is a precursor to the analysis of your experiment. As described in the Section 1.3, real collisions are always subject to some energy dissipation. The approximate conservation of mechanical energy can be expressed as E_f = R · E_i where R is the fraction of energy remaining after the collision. Sketch a plot of E_f vs. E_i for R = 1 and R = 0.5 (on the same plot). If energy is entirely conserved, what is the value of R? 7. (1 pt) In most real collisions, colliding objects are free to rotate about their centers of mass. Imagine a collision between two diatomic molecules as depicted below. Initially, the red molecule is stationary and the blue molecule moves with linear momentum p₁ with no rotational motion. After the collision, both molecules translate in the same direction, but now they also rotate. What caused the molecules to rotate? Is energy still conserved?

Supreeta N.

Transcript

00:01 Hi, in this question at first we will discuss what does it mean for a quantity to be conserved.

00:22 So in physics a conserved quantity means something which does not change.

00:37 It has the same value both before and after an event.

00:57 Secondly, y and conserved particles useful to physicists generally a variable in an equation which represents a conserved quantity is constant after time.

01:38 So it is useful for the physicists to explain the natural filomena by a making use of conserved physical quantities.

01:58 Examples are for kinetic energy where when a ball moving with a velocity v on a surface...

Question

1. What does it mean for a physical quantity to be conserved? Give an example of something that is conserved and something that is not. 2. In general, is kinetic energy conserved? Why or why not? 3. Based on energy conservation, is a "perpetual motion" machine possible? Why or why not?

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