Question

A block is sliding up an incline and slowing due to friction. What is the nature of the frictional force the block exerts on the incline?
a. The same magnitude and direction as the friction force the incline exerts on the block
b. The same magnitude and opposite direction as the friction force the incline exerts on the block
c. The same direction but less than the magnitude of the frictional force the incline exerts on the block
d. The opposite direction but more than the magnitude of the frictional force the incline exerts on the block.
e. The opposite direction but less than the magnitu

Answer 1

the rest of e:e. The opposite direction but less than the magnitude of the frictional force the incline exerts on the block

@Michele_Laino Do you think you could check my answer if you have time? I think it is (B.) because opposite reactions are equal, but since its slowing the friction has to be opposite, is that right?

Answer 2

hint:

R is the friction force, and F is the force exerted by the inclined plane on the block.
Now the motion of the block is possible, since the magnitude of the force F is greater than the magnitude of the force R.
If we have F=R, then the block can not move on the inclined plane
Furthermore, if F<R the block can not miove on the inclined plane

Answer 3

oops...move*

Answer 4

but its going up the plane??

Answer 5

sorry, it is going down the plane!

Answer 6

and its slowing down

Answer 7

yes!

Answer 8

here is the right drawing:

Answer 9

the motion of the block is possible, if F>R.
If F=R then the block can not move on the inclined plane

Answer 10

oh so i got the opposite direction part but in other words your saying that friction has to be greater because its stopping?

Answer 11

the friction force has to be equal to the driving force, so our block can not move on the inclined plane

Answer 12

wait so the forces are equal? Im sorry im confused I was looking at the drawing

Answer 13

we can have three cases:
case #1 F>R--->our block is going up
case #2 F=R---> our block is at the rest, it can not move
case #3 R>F ---> our block is at the rest, it can not move

Answer 14

ok and we have case 1 right?

Answer 15

for example if I apply a force whose magnitude is F= 5,000 Newtons, and the mass of our block is 100 Kg, the coefficietn of friction is 0.2
and the slope of our inclined plane is 30 degrees
ok, in taht case the magnitude of R is given by the subsequent formula:
\[R = \mu \times m \times g \times \cos 30 = 0.2 \times 100 \times 9.81 \times 0.866 = 169.91\;Newton\]
which is less than F=5,000 Newton

Answer 16

that is the case represented by my second drawing

Answer 17

OH ok so R<F, i didnt know R didnt depend on F!

Answer 18

R is independent of F
the force R depends on the mass of the block, on the sliding surfaces, and on the slope of our inclined plane

Answer 19

ok thanks!!!