Gravitation

Physics Part I

Physics

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Two stones are thrown up simultaneously from the edge of a cliff 240 m high with an initial speed of 10 m/s and 40 m/s respectively. Which of the following graph best represents the time variation of relative position of the second stone with respect to the first? (Assume stones do not rebound after hitting the ground and neglect air resistance, take g = 10 m/s^{2} )

C.

The concept of relative motion can be applied to predict the nature of motion of one particle with respect to the other.

Consider the stones thrown up simultaneously as shown in the diagram below.

Considering the motion of the second particle with respect to the first we have relative acceleration

|a^{21}| = |a^{2}-a^{1}| = g-g = 0

Thus, motion of the first particle is straight line with respect to the second particle till the first particle strikes ground at a time given by

Thus, distance covered by the second particle with respect to the first particle in 8s is

S_{12} = (v_{21}) t = (40-10)(8s)

= 30 x 8 = 240m

Similarly, time taken by the second particle to strike the ground is given by

Thus, after the 8s magnitude of relative velocity will increases up to 12 s when the second particle strikes the ground.

The concept of relative motion can be applied to predict the nature of motion of one particle with respect to the other.

Consider the stones thrown up simultaneously as shown in the diagram below.

Considering the motion of the second particle with respect to the first we have relative acceleration

|a^{21}| = |a^{2}-a^{1}| = g-g = 0

Thus, motion of the first particle is straight line with respect to the second particle till the first particle strikes ground at a time given by

Thus, distance covered by the second particle with respect to the first particle in 8s is

S_{12} = (v_{21}) t = (40-10)(8s)

= 30 x 8 = 240m

Similarly, time taken by the second particle to strike the ground is given by

Thus, after the 8s magnitude of relative velocity will increases up to 12 s when the second particle strikes the ground.

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What is Geocentric theory?

According to the geocentric theory, all the astronomical bodies like the moon, the sun and stars revolve around the earth, and the earth is at the centre of the universe.

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What is Heliocentric theory?

According to the Heliocentric theory, the sun is at the centre and various planets revolve around the sun at their axis.

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The position co-ordinates of two particles of masses m_{1} and m_{2}are (x_{1}, y_{1}, z_{1}) and (x_{2}, y_{2}, z_{2}) respectively. Find the coordinates of the centre of mass.

The position vectors of masses m

Let the position coordinates of the centre of mass be (X, Y, Z).

Therefore the position vector of centre of mass is,

Since,

Comparing the coefficients of , we get

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What is the celestial sphere?

At night, if we see the planets and the stars in the sky, all appear to lie in the hemisphere (rest of the hemisphere we are unable to see because of being on the other side of the earth). This sphere is called the celestial sphere.

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