Need help with Parts B, C, D, E We usually ignore the kinetic energy of the movi
ID: 2246267 • Letter: N
Question
Need help with Parts B, C, D, E
We usually ignore the kinetic energy of the moving coils of a spring, but let's try to get a reasonable approximation to this. Consider a spring of mass M, equilibrium length L 0, and spring constant k. The work done to stretch or compress the spring by a distance L is 1 / 2 kX2, where X = L - L0. Consider a spring, as described above, that has one end fixed and the other and moving with speed v. Assume that the speed of points along the length of the spring varies linearly with distance l from the fixed end. Assume also that the mass M of the spring is distributed uniformly along the length of the spring. Calculate the kinetic energy of the spring in terms of M and v. (Hint: Divide the spring into pieces of length dl; find the speed of each piece in terms of l,v, and L; find the mass of each piece in terms of dl, M, and L; and integrate from 0 to L. The result is not 1 / 2 Mv2, since not all of the spring moves with the same speed) K = Mv 2 / 6 In a spring gun, a spring of mass 0.236kg and force constant 3100N / m is compressed 2.40cm from its unstretched length. When the trigger is pulled, the spring pushes horizontally on a 4.2 times 10 - 2kg ball. The work done by friction is negligible. Calculate the ball's speed when the spring reaches its uncompressed length ignoring the mass of the spring. Express your answer using two significant figures. Calculate the ball's speed when the spnng reaches its uncompressed length including, using the results of part A, the mass of the spring. Express your answer using two significant figures. In part C, what is the final kinetic energy of the ball ? Express your answer using two significant figures. In part C, what is the final kinetic energy of the spinng ? Express your answer using two significant figures.Explanation / Answer
B) Potenital energy,U = 1/2 kx^2 = 1/2 *3100*(.024)^2 = 0.8928 J
when at uncompressed length U is converted into kintetic energy, K
K = 1/2 mv^2 => v = sqrt (2K / m)
v = sqrt(2*.8928/0.042) = 6.52m/s
C) Using results of part A
U = K = (Mv^2)/6
v = sqrt (6K / m) = 11.29 m/s
D) kinetic energy of ball, K = 1/2 mv^2 = 1/2 *.042*(11.29)^2
K = 2.678 J
E) 0.042 * 11.29 = 0.236 * v
v = 2.009 m/s
K = 1/2 mv^2 = 0.4763 J