Two packages stacked on one another

Homework Statement

A delivery van has two packages left that are stacked one on top of another. The upper packages
has a mass of 4.0 kg and is a poorly packaged glass vase, while the lower package has a mass
6.5 kg. The coefficient of static friction between the two packages is 0.211 and the lower box is
fixed to the floor of the van. Since the delivery person is late, he has been accelerating quickly
whenever he has stopped and started (at lights, stop sign etc.), however he never exceeds the
town's speed limit of 60 km/h. What is the minimum amount of time it takes for him to reach
his top speed while still keeping the vase from breaking (sliding off the top box).

Homework Equations

friction= coefficient x contact force
fnet=ma

The Attempt at a Solution

friction = 0.211x 4kg x 9.81
= 8.24N
what do i do next?

Last edited:

$F_{fr top} = (m_{top})(a) = (u_s)(F_{N top})$