How does tightening a string on a guitar affect its natural frequency?

Abody of weight 60 kg is standing in a lift the lift going upward with a uniform velocity of 4.9 metre per second slows down and stops in two seconds then apparent weight of the body during the slow down process is

Occurs when an energy source transfers heat directly to another subject space; an example would be an object becoming warm by sitting in the sunshine

In a good thermo flask the main cause of heat loss is