The question is as follows: An object of mass m=1 follows the trajectory: r(t) = 4 ln(t) i + 6t1/2 j + 2t k Calculate the force acting on the object and hence find work done between t=1 and t=2. I know that Force = Mass * Acceleration Therefore, F(t) = 1 * a(t) I also know that a(t) = r(t)'' After differentiating I end up with r(t)'' = -4t-2 i - 3/2 t-3/2 j So I've ended up with F(t) = -4t-2 i - 3/2 t-3/2 j Is that my final answer for the force acting on the object, do I leave it in vector form? For the work done part, I know that Work Done = Force x Distance I have force and displacement in vector form but I don't know how to end up with a completely numerical value as I've got a time interval for t, I'm assuming there will be some sort of integration involved. Can someone please tell me if I have done the first part correctly (calculating the force acting on the object) and if so how can I use this along with the conditions t=1 and t=2 to calculate work done? Thanks!