We can use the textbook results for head-on elastic collisions to analyze the recoil of the earth when a ball bounces off a wall embedded in the earth. suppose a professional baseball pitcher hurls a baseball ( 155 grams = 0.155 kg) with a speed of 104 miles per hour ( 45.8 m/s) at a wall, and the ball bounces back with little loss of kinetic energy. (a) what is the recoil speed of the earth ( 6 × 1024 kg)?