Originally Posted by **maserati** A 500 g glider sliding on friction-less track with speed 0.2 m/s hits spring bumper a max distance 0.5 cm before rebounding. What's the spring constant?
So, I calculated the kinetic energy first: 0.5*0.5 kg*0.2 m/s= 0.05 J.
Then calculated potential energy: 0.5 kg*9.8 m/s^2*0.005 m = 0.0245 J.
Then subtract each other: 0.05 J-0.0245 J= 0.0255 J.
Then I set up 0.0255 J = 0.5 Ks (spring constant) * (0.005 m)^2 and I solved for Ks and it's 2040 J/m^2.
It turned out wrong, can anyone tell me what is wrong with my logic here? |

In your first line you have 0.5 * 0.5 * 0.2. It should be 0.5 * 0.5 * 0.5 * (0.2)^2

Also, the

*spring* potential energy is (1/2) * k * x^2. It has nothing at all to do with g!!!

I'd approach this from the work-energy theorem directly. That is

The work done is work done by the spring on the glider, thus is (1/2)kx^2. The change in kinetic energy of the glider is (1/2)mv^2. Thus we have

Can you finish it from here?

-Dan