posted by Ellie .
Two 30kg children in a 20 kg cart are stationary at the top of a hill. They start rolling down the 80m tall hill and they are traveling at 30 km h-1 when they reach the bottom. (The cart had brakes!) How much work was done on the cart by friction during its travel down the hill? (Note: the use of the word on and remember to specify the sign of the work done.)
plese help me to answer this proplem