# 2 Block Push

## Description

Two
blocks are pushed by identical forces, each starting at rest at the first
vertical rectangle (start). The mass m_{1}=2m_{2}.

## Question

Which object has the greater kinetic energy when it reaches the second
vertical rectangle (finish)?

## Instructor Resources

###### Reference: See Giancoli-PA: 6-3, Giancoli-SE: 7-4.

###### Answer:
The kinetic energies are identical. This is a good problem to ask in the middle
of discussing the work-energy theorem. Typical student reaction is that the
second mass has a greater velocity and therefore has the greater kinetic energy.
While the second mass does have the greater velocity at the finish, it is not
double the velocity of m_{1}. Students can see this from Newton’s
second law and kinematics, although it is a little tedious. The correct
rationale here is to recognize that the work done by the force on each mass is
identical as the displacements are identical.

###### Script Author: Mario Belloni