7- A 1-kg object strikes a spring on a frictionless horizontal plane with a velocity of 10m/s, as shown in the figure, and returns with the same velocity. If the object and the spring interact for Δt=2 s, find the change in the momentum of the object.
a) 10kg.m/s
b) 20kg.m/s
c) 30kg.m/s
d) 40kg.m/s
