# ex. 4

```4-A block of mass m = 2kg is released from rest
from the top A of an inclined plane AB = d that
makes an angle α with the horizontal. The force
of friction along AB has a constant magnitude
of 2N.
Take the horizontal level of B as a gravitational
potential energy reference for the system
[block-Earth].
The adjacent figure (2) shows the variation with
time, of two types of energy out of the three
types:
kinetic, potential and mechanical between A
and B. Examine carefully the two figures then
1.a) Curve (2) represents the gravitational
potential energy. Justify.
b) Curve (1) does not reresent the kinetic
energy. Justify.
2. a) Determine the value of the height of A
above B,,,,(h = ?)
b) What is the value of the mechanical
energy at B
c) Deduce the values of d and α .
P.E
d) Determine the kinetic energy at B and its
speed then.
K.E
3. Determine the speed of the block as it
passes in the midpoint of AB.
4. Complete the following table then plot on the same figure (2) the graph of the kinetic energy
of the block.
t
0
M.E
+
1
2
3
4
5
```