Class 9 Physics Gravitation

$6. At what distance from the centre of the earth does the gravitational acceleration have one half the value that It has on the earths surface?$

$2. A hoop and disc have same mass and radius. Their rotational K.E are related by an equation.a) K . E_{\text {hoop }}=K . E_{\text {disc }} b) K . E_{\text {hoop }}=2 K . E_{\text {disc }} c) K . E_{\text {hoop }}=1 / 2 K . E_{\text {disc }} d) K . E_{\text {hoop }}=4 K . E_{\text {disc }}$

$23. A cyclist cycling around a circular racing track skids becausea) The centripetal force upon him is less than limiting frictionb) The centripetal force upon him is greater than limiting frictionc) The centripetal force upon him is equal to the limiting frictiond) The friction between the tyres of the cycle and road vanishes$

$45. The value of gravitational constant was determined bya) Newtonb) Keplerc) Cavendishd) Maxwell$

$5. Radius of geo-stationary orbit form center of earth is nearly.a) 42000 \mathrm{~km} b) 36000 \mathrm{~km} c) 24000 \mathrm{~km} d) 18000 \mathrm{~km}$

$40. The sun exerts a forces of attraction on the planets for keeping them in theira) Axesb) Spin-motionc) Orbitsd) None of them$