A horizontal force acting on a 2kg cart varies with displacement as F(x)=10−3x (in newtons), where x is in metres. The cart starts from rest at x=0 on a frictionless track. Its speed when it reaches x=3m is approximately
a) 6.4m s−1
b) 3.0m s−1
c) 4.1m s−1
d) 5.5m s−1