as per the equation: p(momentum)= (mass x velocity) the answer is 680 kg*m/s.
the net force vector will be in forward direction. therefore the correct answer is option (d).
since the skier pushes himself along the snow on flat ground and he feels air resistance, he will only feels air resistance when he starts moving (unless wind is blowing in opposite direction). the net force vector is dependent on the amount of force applied by the skier here we assume that skier continues to move in forward direction. the net force vector will act in the direction of acceleration, since the skier continues to move in the forward direction, therefore the net force vector will also point in the forward direction.
a longitudinal wave is a wave that vibrates the medium in the same direction in which the wave energy travels.
the answer would be c.
earthquakes are normally associated when two tectonic plates move away from each other causing a rift in the plate and you get an earthquake.