 #1
jolly_math
 42
 5
 Homework Statement:
 Two children are playing a game in which they try to hit a small box on the floor with a marble fired from a springloaded gun that is mounted on a table. The target box is 2.20 m horizontally from the edge of the table. Bobby compresses the spring 1.10 cm, but the marble falls 27.0 cm short. How far should Rhoda compress the spring to score a hit?
 Relevant Equations:

U(x) = (1/2)kx^2
KE = (1/2)mv^2
K_{i} + U_{i} = K_{f} + U_{f}
1/2)kx^{2} = (1/2)mv_{f}^{2}, but W = (1/2)mv_{f}^{2} = F∆d, so
1/2)kx^2 = F∆d.
The solution says that I should just substitute v as d/t. But could anyone explain why my reasoning is wrong? Thanks.
1/2)kx^{2} = (1/2)mv_{f}^{2}, but W = (1/2)mv_{f}^{2} = F∆d, so
1/2)kx^2 = F∆d.
The solution says that I should just substitute v as d/t. But could anyone explain why my reasoning is wrong? Thanks.