How Much Force Does Water Apply to a Sandbag Dropped from a Hot-Air Balloon?

[Brittykitty]

At an altitude of 315 m above a lake, a hot-air balloon pilot drops a 2.50 kg sandbag. If the bag comes to a stop 4.50 m below the surface of the lake, what force was applied by the water on it?

Mass:2.50kg
velocity: 2.50kg*9.81m/s=61.31?

I can't remember how to figure out what the time would be?

 

[rock.freak667]

It's easier to use a conservation of energy method. So try that instead