A body of mass m=10−2 kg is moving in a medium and experiences a frictional force F=−kv2 . Its initial speed is v0=10 ms −1 . If, after 10 s, its energy is 81mv02 , the value of k will be:
(a) 10−4 kg m −1
(b) 10−1 kg m −1 s −1
(c) 10−3 kg m −1
(d) 10−3 kg s −1