Why are the nuclei of the heavier elements radioactive and not the lighter elements nuclei?

Orque can be calculated by multiplying the force (n) applied at 90? to the lever arm at a distance (m) from the pivot point (point of rotation), the compound si unit for the torque is n? m. if the force (at 90? to the lever arm) applied is 15 n and it is applied at 2.0 m from the pivot point (point of rotation), what is the torque on the lever?

Emagnitude of the electrical force acting between a +2.4 ×  10–8  c charge and a +1.8 ×  10–6  c charge that are separated by 0.008 m is    n, rounded to the tenths place.

Four identical lab carts each have a mass of 200 kg. different masses are added to the carts and the velocities are measured. all carts move to the right.