Answer:
Explanation:
In the whole process , potential energy of the cart is converted into kinetic energy . At the top of the vertical loop , the whole of potential energy is regained and kinetic energy becomes zero if we release the cart from a height of 2R because difference of height between lowest and highest point of motion is 2R . In that case kinetic energy at top = 0 , velocity v = 0
At the top , weight mg is acting which is providing centripetal force . So cart must have some velocity at the top . If it be v
mv²/R = mg
v = √ gR .
For that purpose , the cart must be released from a height greater than 2R .
The extra height beyond 2R will make the velocity at the top non-zero.