Snowboarding cautiously down a steep slope at a speed of 7.0 m/s, Sarah, whose mass is 50.0-kilograms, is
afraid she won't have enough speed to travel up a slight uphill grade ahead of her. She extends her hand, as
her friend Trevor, having a mass of 100.0-kilograms is about to pass her traveling at 16 m/s. If Trevor
grabs her hand, calculate the speed at which the friends will be sliding.