Question

A wrecking ball is swinging at just the right height so that the student can stand at the bottom of the trajectory (lowest point) and grab onto the ball to swing – something that is just way too tempting for this inquisitive student. In order to justify invading the construction zone, before the student jumps on she attaches a magnet to an accelerometer and sticks the accelerometer onto the iron ball. The maximum velocity reading before she jumps on is 1.98m/s. Once she is on the ball, she reads that the maximum speed of herself and the ball together is 1.90 m/s. What is the mass of the wrecking ball?

length of cable of wrecking ball is 13m

Answer 1

conservation of momentum:
initial=final
M*1.98=(M+m)1.90
and you are looking to solve for Mass wrecking ball, but it was not given the mass of the idiot student, m.

So....I guess I would do an estimate by making an estimate for the idiot student's mass, say, 60kg
with that
M/(M+60)=1.90/1.98
or
M=(1.90/1.98)(M+60)
M(.08)=(1.90*60/1.98)
and you can solve M IF m=60kg