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A numerical from Projectile motion, friction and more

Hale asked:

One side of the roof of a building slopes up at 33.5°. A roofer kicks a round, flat rock that has been thrown onto the roof by a neighborhood child. The rock slides straight up the incline with an initial speed of 15.0 m/s. The coefficient of kinetic friction between the rock and the roof is 0.430. The rock slides 10.0 m up the roof to its peak. It crosses the ridge and goes into free fall, following a parabolic trajectory above the far side of the roof, with negligible air resistance. Determine the maximum height the rock reaches above the point where it was kicked.

(The question is left for visitors to answer.)

An Idea for Cycle Rickshaw

Sumit Asks:

   While seeing a rickshaw puller struggling to pull heavy weight,I wondered if the load carried by him can be reduced for carrying same weight people.Since the load carried by him is dependent on the horizontal component of frictional force (i.e,µ.mgsinØ) ,cant we apply a spring in the rickshaw so that the effective weight will decrease and hence the load carried by him?

How can the electric current in a circuit be kept continuous?

Susmita asked:

  1. What is Current?
  2. How can electric current in a circuit be kept continuous?



The word current means flow.

Electric Current refers to charges in motion. The most common way of producing current is by applying a potential difference across the terminals of a conductor. Then the free electrons in the conductor drifts towards the positive terminal.

The current in the circuit can be kept continuous by providing a constant potential difference between two points of the circuit. This is usually done by connecting the ends of the circuit to the terminals of an electrochemical cell (which converts chemical energy to electrical energy) or a dynamo (which converts mechanical energy to electrical energy)

Please refer the following links for more information

why earth moves in an elliptical orbit instead of circular one?

Zeenath PV asked:

why earth moves in an elliptical orbit instead of circular one?


image Please note that ELLIPSE is the more general form for an orbit and CIRCLE is a speacial case of ellipse.

So, it is more general way of saying that the orbits are elliptical. If it were circular, we would have more trouble explaining why they are perfect circles.

The situation where the Sun, for instance, would be exactly in the center of a perfectly circular planetary orbit couldn’t happen in our Solar System since there are other planets that would gravitationally affect the orbit and cause it to be immediately non-circular by pulling the object to one side or the other.  Any other stable orbit type than a perfectly circular one turns out to be an elliptical orbit.

Read more at : http://www.astro-tom.com/technical_data/why_elliptical.htm

How earths tilt causes seasonal change?

Zeenath PV asked: how earths tilt causes seasonal change?


image The climate on earth is mainly determined by the distance from sun and how much sunlight (and heat radiations) is received by earth. The relative duration of day and night as well as the climate is greatly dependant on the tilt of the earth’s axis with respect to its plane of orbit around sun and the elliptical shape of earth

Please follow these links to read more:

  1. http://www.msnbc.msn.com/id/3077384/
  2. http://en.wikipedia.org/wiki/Season
  3. http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980211f.html
  4. http://www.eoearth.org/article/Causes_of_climate_change

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