Question

An electron's position is given by r = 4.00t i - 6.00t^2 j + 5.00 k, with t in seconds and r in meters. In unit-vector notation, what is the electron's velocity? (Answer in terms of i, j, k, t.)What is v in unit-vector notation at t = 8 seconds? What is the magnitude of v at t = 8 seconds? What angle does v make with the positive direction of the x axis at t = 8 seconds?

velocity= dr/dt= 4i-12tj

angle= arctan -12t/4

In unit-vector notation, what is the electron's velocity v(t)? (Answer in terms of i, j, k, and t.)