What is the acceleration if the mass of the ball in question 1 is tripled and two forces
are applied to the ball, one of 2.3 N and
another of 1.7 N. in the same direction?

the part of the wave he is travelling on is the crest

  distance on the y-axis and time on the x-axis.

explanation:

the instantaneous velocity = change in position/time taken

the slope of the graph should give instantaneous velocity.

  slope of a graph = change in value of y -axis / change in values of x -axis

  comparing both the equations

    change in value of y -axis = change in position

  change in values of x -axis = time taken

so position values should be on the y axis and time values should be on the x axis.

distance on the y-axis and time on the x-axis.