An airplane is sent on a rescue mission to help a stranded explorer near the South Pole....

An airplane is sent on a rescue mission to help a stranded explorer near the South Pole. The plane cannot land, but instead drops a supply package of mass m = 60 kg while it is flying horizontally with speed The supply package drops onto a waiting sled that is initially at rest (Fig. P7.39). After the package lands in the sled, the speed of the sled plus package is found to be 30 m/s. What is the mass of the sled? Ignore air drag.