We have an electron pulse of width 1 nanosecond and with kinetic energy of 1keV. We have to calculate Δx and Δp. I have a question regarding this problem. If they give us the kinetic energy of the electron pulse then we know exactly the momentum right? And so the uncertainty of momentum would be 0 and therefore Δx=∞ for the uncertainty principle ΔxΔp≥h. However I feel this reasoning is incorrect otherwise the problem would be trivial.