GRAVITATION
Very Short Question Answers
Q1. State the unit and dimension of the universal gravitational constant (G).
Ans. S.I Unit- $\,\,Nm^{2}/kg^{2}$ Dimensional Formula :$\,\,[M^{-1}\,L^{3}\,T^{-2}\,]$
Q2. State the vector form of Newton's law of gravitation.
Ans. Gravitational force $F=-G \frac {m_{1}m_{2}}{r^{2}}\hat{r} \:\:(or) \:\:F=-G \frac {m_{1}m_{2}}{r^{3}}\vec{r}$
Q3. If the gravitational force of Earth on the Moon is F. what is the gravitational force of moon on earth? Do these forces form an action-reaction pair?
Ans.- The gravitational force of the moon on the earth = -F
- These two forces are equal and opposite direction. Hence, they form action and reaction pair
Q4. What would be the change in acceleration due to gravity (g) at the surface, if the radius of Earth decreases by 2% keeping the mass of Earth constant?
Ans. $We\, know \, that\, \frac{\bigtriangleup R}{R}=-2%$
$Change\, in\, acceleration \,due\,to\,gravity\,$
$\frac{\bigtriangleup g}{g}=-2\times \frac{\bigtriangleup R}{R}=-2\times-2=4$
Q5. As we go from one planet to another, how will a) the mass and b) the weight of a body change?
Ans.- The mass of the body is always constant.
- Weight of the body also changes.
Q6. Keeping the length of a simple pendulum constant, will the time period be the same on all planets? Support your answer with reason.
Ans. $Time\,Period \,\: T \propto \frac{1} {\sqrt g} $
Hence, the gravitational force varies from planet to planet, so the time period also changes from planet to planet.
Q7. Give the equation for the value of g at a depth 'd' from the surface of Earth. What is the value of 'g at the centre of Earth?
Q8. What are the factors that make 'g the least at the equator and maximum at the poles?
Ans. At Equator: i) equatorial radius of the earth is maximum. ii) latitude, φ=0°
At Poles: i) polar radius of the earth is minimum ii) latitude φ=90°
(Or) i) shape of the earth ii) rotation of the earth.
Q9. Hydrogen is in abundance around the sun but not around earth. Explain.
Ans. The escape velocity on the sun is greater than r.m.s velocity of hydrogen.But the escape velocity on earth is less than the r.m.s velocity of hydrogen. So, hydrogen is in abundance around the sun and less around the earth.
Q10. What is the time period of revolution of a geostationary satellite? Does it rotate from West to East or from East to West?.
Ans. Time period of revolution of a geostationary satellite is 24 hours. It rotates from west to east.
Q11. What are polar satellites?
Ans. A satellite that revolves in a polar orbit is called a polar satellite.A polar orbit passes over north and south poles of the earth.Time period (T) = 100 min.