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# Monthly Archives: April 2016

## Space Time Curvature and the TRampoline analogy

In the trampoline demonstration representing space-time and gravity, it is obviously the friction between the trampoline and the ball that determines the path of the ball. Friction is a physical interaction, so space-time has to physically interact with matter for this demonstration to be a plausible description of what is happening actually. My question is, what is or what causes that physical interaction or “friction” between space-time and matter when space-time is curved?? Thank you

The trampoline is just an analogy to understand the phenomenon. Gravity is like the depression of the trampoline causing a curvature in the space time continuum.

## Calculate momentum

What is the momentum of a 2,000kg car traveling with a speed of 25 m/s?

Momentum is the product of mass and velocity. Magnitude of momentum may be calculated by multiplying mass and speed.
So, the magnitude of momentum of the car = 2000×25=50000 kg m/s

## Conservation of momentum – problem

A ring of radius ‘R’ and mass ‘M’ lies on its side on a frictionless table. A bug of mass ‘m’ rests on the ring. Bug starts walking on the ring with constant speed ‘v’ relative to the ring. Describe the motion of ring relative to ground frame.

(In some questions ring being pivoted, but here not, ring is free to move any way horizontally). Thanks.

(The pivoted ring problem is solved here)

## A Question from Inertia and Motion

A person is standing on the floor of a train moving with constant speed and continues to do so then if that person jumps for 2-3 seconds then will he land on same spot or behind that spot

Posted by Lokesh

## Question from image formation by a plane mirror

if a ball is located 4 meters in front of a mirror, what distance separates the object from the image? please Use your diagram to aid your answer.

1. An energy saver light bulb of 11 W gives the same illumination as a conventional 60W light bulb. (a) If a typical light bulb is used on average for five hours a day, how much energy is saved per year by one light-bulb? (b) If each household used eight such light-bulbs, ad there are 20 million households in a country, how much energy would that country save annually?
2. A system consists of a gas inside a cylinder. Inside the cylinder there is a 10ohm resistor connected to an electrical circuit through which a current can pass. A mass of 0.1 kg is placed on the piston which drops by 0.2m and comes to rest. A current of 0.1 A is passed through the 10 ohm resistor for 2s. What is the change in the internal energy of the system when it has reached equilibrium?
3. An explosive liquid at temperature 300 K contains a spherical bubbles of radius 5 mm, full of its vapour. When a mechanical shock to the liquid causes adiabatic compression of the bubble, what radius of the bubble is required for combustion of the vapour, given that the vapour ignites spontaneously at 1100 C? The ratio Cv/nR is 3 for the vapour.

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