Answer:
To solve this problem, we can use the formula for the potential energy stored in a stretched spring or rubber band: U = (1/2) k x^2
where U is the potential energy, k is the spring constant, and x is the amount of stretch.
We can rearrange this formula to solve for k: k = 2 U / x^2
The velocity of the pebble can be found using conservation of energy:
(1/2) m v^2 = U
where m is the mass of the pebble and v is its velocity.
Rearranging this formula, we get: v = sqrt(2 U / m)
We can combine these formulas to solve for the length of the rubber band:
k = (4 U) / (0.25 L^2)
v = sqrt((8 U) / (0.006))
where L is the original length of the rubber band.
Since the width and thickness of the rubber band are given, we can calculate its cross-sectional area:
A = (9 mm) x (1.55 mm) = 13.95 mm^2 = 1.395 x 10^-5 m^2
Using the Young's modulus given in the problem, we can calculate the spring constant: k = (A / L) x (Y / 4)
where Y is the Young's modulus.
The formula for k above, we get: (4 A Y / L^3) x (U / 0.25) = 0.006 v^2
Solving for L, we get: L = (4 A Y U / 0.006 v^2)^1/3
Substituting the given values and solving, we get: L = 34.86 cm
Therefore, the length of the rubber band should be approximately 34.86 cm to achieve the desired velocity of the pebble