## Conceptual Physics (12th Edition)

a. Impulse equals force multiplied by time. The 3 impulses delivered, in the order ABC, are: $$(100 N)(3 s) = 300 N s$$ $$(75 N)(3 s) = 225 N s$$ $$(50 N)(3 s) = 150 N s$$ b. Impulse equals the change in momentum. c. The final momentum, mv, is the same as the change in momentum, which is the impulse, because the crates started from rest. Find the final speed by dividing impulse and mass. In the order ABC, the final speeds are: $$\frac{300 N \cdot s}{30 kg} = 10 \frac{m}{s}, \frac{225 N \cdot s}{20 kg} = 11.25 \frac{m}{s}, \frac{150 N \cdot s}{10 kg} = 15 \frac{m}{s}$$ d. The final momentum, mv, is the same as the change in momentum, which is the impulse, because the crates started from rest.