On a cold winter morning, a child sits on a sled resting on smooth ice. When the 9.60- sled is pulled with a horizontal force of 35.0 , it begins to move with an acceleration of 2.10 .
The 21.0- child accelerates too, but with a smaller acceleration than that of the sled. Thus, the child moves forward relative to the ice, but slides backward relative to the sled.
Find the acceleration of the child relative to the ice.