A paddle ball toy consists of a flat wooden paddle and a small rubber ball that are attached to each other by an elastic band.

Question

use the approximation that v avg = Pf / m for each time step

A paddle ball toy consists of a flat wooden paddle and a small rubber ball that are attached to each other by an elastic band. you have a paddle ball toy for which the mass of the ball is 0.014 kg, the stiffness of the elastic band is 0.875 N/m, and the relaxed length of the elastic band is 0.270 m. You are holding the paddle so that the ball hangs suspended under it, when your cat comes along and bats the ball around, setting it into motion. At a particular instant, the momentum of the ball is (-0.02, -0.01, -0.02) and the moving ball is at location (-0.2, -0.61, 0) relative to an origin located at the point where the elastic band is attached to the paddle.

part 1: Determine the position of the ball 0.1 s later, using a delta t of 0.1

r = (-0.2707, -0.5586, -.143) (counted correct by my homework)

fnet = (0.101, .172, 0)

pf = pi + fnet * delta t = (-0.0099, -0.0072, -0.02)

v = (-0.707, 0.514, -1.43)

rf = ri + v averg * delta t = r = (-0.2707, -0.5586, -.143)

Part 2: starting with the same initial position (-0.2, -0.61, 0) and momentum (-0.02, -0.01, -0.02) determine the position of the ball 0.1s later using a delta t of 0.05s.

I repeat part 1, but get the wrong answer

fnet = (0.101, 0.172, 0) m =.014

pf = pi + fnet *delta t

(-.02, -.01, -.02) + (0.101, .172, 0) *(.05) = (-0.01495, -.0014, -0.02)

v avg = p/m = (-0.01495, -.0014, -0.02) / .014 = (-1.07, -0.1, -1.43)

rf =ri + v avg * delta t = (-0.2, -0.61, 0) + (-1.07, -0.1, -1.43) * (.05) = (-.2535, -.615, -.0715)

It counted (-.2535, -.615, -.0715). Is there some thing I'm missing or some other way to do it?

Answer 1