A radioactive nucleus at rest decays into a second nucleus, an electron, and a neutrino. The electron and neutrino are emitted at right angles and have momenta of 9.90×10−23 kg⋅m/s and, 6.85×10−23 kg⋅m/s respectively.
a. Determine the magnitude of the momentum of the second (recoiling) nucleus.
b. Determine the direction of the momentum of the second (recoiling) nucleus. Assume that the neutrino and the electron move along −x and −y axes respectively.

Protons and neutrons are found within the nucleus of an atom

Idon’t quite understand this problem

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".