Which of the following graphs best represents the kinetic energy K of the object as a function of time?

Question

An object of mass m is initially at rest and free to move without friction in any direction in the xy-plane. A constant net force of magnitude F directed in the +x direction acts on the object for 1 s. Immediately thereafter a constant net force of the same magnitude F directed in the +y direction acts on the object for 1 s. After this, no forces act on the object.

Which of the following graphs best represents the kinetic energy K of the object as a function of time?

Answer 1

Correct option

  

Kinetic energy is not a vector and the total resultant velocity should be used to determine the KE. For the 1^st second the object gains speed at a uniform rate in the x direction and since KE is proportional to v² we should get a parabola. However, when the 2^nd second starts the new gains in velocity occur only in the y direction and are at smaller values so the gains essentially start over their parabolic trend as shown in graph B