physics
posted by Garcia .
When a spacecraft travels from Earth to the Moon, the gravitational force from Earth initially opposes this journey. Eventually, the spacecraft reaches a point where the Moon's gravitational attraction overcomes the Earth's gravity. How far from Earth must the spacecraft be for the gravitational forces from the Moon and Earth to just cancel?

A hockey puck is hit on a frozen lake and starts moving with a speed of 14.4 m/s. 3.0 seconds later, its speed is 7.3 m/s.
(a) What is its average acceleration?