A 0.2 kg disc slides down from smooth track of height 1.8m. It arrives at a rough 1 kg block resting on a smooth surface. The friction between them is 1.2N. Find the distance travelled by the disc on the block before it comes to rest relative to the block.
The Attempt at a Solution
use observer frame:
then I use conservation of linear momentum, because only internal forces.
f=1.2N to right on the block, to left on the disc
a of disc=-6m/s^2
a of block= 1 m/s^2
for the disc, v^2-u^2=2as
for the block,
so it moves 2.41 m on the surface
but when I find the time required
for the disc, v=u+at
for the block
They are different?
I know my answer of 2.41 m must be wrong, but where is my mistakes?