When a planet moves around the sun
a) its angular momentum remains constant
b) it moves faster when it is near to the sun
c) its total energy increases when it goes near to the sun
d) its potential energy decreases when it goes near to the sun

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only b,c & d are true

only a,b & d are true

only a&b are true

only b&c are true

answer is C.

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Detailed Solution

Since gravitational force of attraction of sun on the planet passes though the centre of sun , it produces no moment about the centre of sun.So angular momentum of the planet about the centre of sun is conserved.At perigee , L =mvr = constant.Since apogee r is minimum , v is maximum and KE (1/2 mV²) is also maximum.Also , KE +PE = TE = Constant.So PE is maximum at perigee.

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