Question

What is the coefficient of friction between your block and the floor? SHOW ALL WORK.
What I know:
t=1.06s
d=1.87m
m=0.132kg
initial velocity of the block=3.53 m/s
acceleration of the block, as it slid to rest=-3.33 m/s^2
force of friction acting on the block during its slide=-0.44N

Answer 1

Draw a free body diagram, but its not necessary here.

To find the force of friction, use F = ma. You know a and m.

Force of friction is u*Normal force. Normal force will be equal to the weight, mg, since i'm assuming it's a flat surface

Answer 2

Is it -0.44N=u*(0.132)(9.81) and then I solve for u?

Answer 3

Yup!

Answer 4

Oh okay! Um Part 2 says: If your block slid across a surface with a coefficient of kinetic friction of 0.25, how far would it have slid, assuming that it started with the same initial velocity from #1 (3.53 m/s)?

Answer 5

Use F = ma to find a (use the same method, umg to find friction force F)

then use one of the motion equations to find the distance, like \[\Large v_f^2 = v_i^2 + 2a \Delta x\]

Answer 6

I don't get it. :/

Answer 7

Find acceleration, using F=ma. F is the force of friction, umg. Same thing as above, with u=0.25

Answer 8

umg = ma which you can solve for a

Answer 9

would it be 3.33 m/s^2?

Answer 10

umg = ma
cancel off m's
a = ug = 0.25 (9.81)

Answer 11

oh yeah I got it. I put in the wrong number. :P

Answer 12

so it's 2.4525 m/s^2

Answer 13

Now use the equation above... or some other equation you prefer, using a, to find distance travelled

initial v= 3.53 m/s
a = 2.4525 m/s^2

Answer 14

-1.44m?

Answer 15

Using the \[\Large v_f^2 = v_i^2 + 2a \Delta x\] vf = 0. vi=3.53. a=2.4525. Solve for the distance delta x

Answer 16

did I do it wrong? I thought I did that. umm.... maybe I'll try again.

Answer 17

Make sure you square the velocity.

Answer 18

oh. -2.54m?

Answer 19

yep :) but it should be positive. It's in the same direction as velocity. But its no big deal as long as you know the direction.

Answer 20

Thanks! I always mess up the calculations when I do them without a calculator.

Answer 21

no prob. Good job!