# physics

posted by .

A moving 2.8 kg block collides with a horizontal spring whose spring constant is 215 N/m (see figure). The block compresses the spring a maximum distance of 11.5 cm from its rest position. The coefficient of kinetic friction between the block and the horizontal surface is 0.48

How much mechanical energy is being dissipated by the force of friction while the block is being brought to rest by the spring?
I found the work done by the spring -1.42J

• physics -

I get the friction work to be
(friction force)(distance moved) =
(0.48)(2.8)(9.8)(0.115) = 1.52 J

You don't need the spring constant to get the answer.

• physics -

the next part is
What is the speed of the block when it hits the spring?
i did
1.42=.5mv^2(final)-.5mv^2(initail)
The final velocity woulf be zero
so
1.42=.5(2.8)v^2
v=1.01
im not sure what i did wrong

• physics -

Initial KE = (stored spring PE when stopped) + friction work
(1/2)MV^2 = (1/2)kX^2 + 1.52 J

Now recalculate V. Include the units. Numbers by themselves, without units, are useless.

• physics -

thanks

• physics -

Why is friction work positive????