In the reality television show \"Amazing Race,\" a contestant is firing 12 kg wa
ID: 1784244 • Letter: I
Question
In the reality television show "Amazing Race," a contestant is firing 12 kg watermelons from a slingshot to hit targets down the field. The slingshot is stretched from its equilibrium length by a distance of 2.00 m, and the watermelon is at ground level, 0.50 m below the launch point. The targets are at ground level 18.0 m horizontally away from the launch point. Calculate the spring constant of the slingshot (in N/m). (Assume the angle that the watermelon's velocity makes with the horizontal at the launch point is the same as the angle the slingshot makes with the horizontal when pulled back. Also assume the equilibrium length of the slingshot is negligible.)
Explanation / Answer
vy = sqrt [2 g h] = sqrt [2 * 9 .8 * 0.5] = 3.13 m/s
vx = g d / sqrt [2 g y0] = 9.8 * 18 / (sqrt (2 * 9.8 * 0.5)) = 56.35 m/s
v = sqrt [3.132 + 56.352] = 56.44 m/s
From conservation, mg h + 1/2 k x2 = 1/2 m v2
k = 2 (1/2 m v2 - mgh) / x2
= [2 * (0.5 * 12 * 56.442 - 12 * 9.8 * 0.5)] / 22
spring constant = 9527 N/m