A block of weight mg sits on an inclined plane as shown in (Figure 1) . A force of magnitude F1 is applied to pull the block up
1 answer:
Answer:
W = (F1 - mg sin θ) L, W = -μ mg cos θ L
Explanation:
Let's use Newton's second law to find the friction force. In these problems the x axis is taken parallel to the plane and the y axis perpendicular to the plane
Y Axis
N - =
N = W_{y}
X axis
F1 - fr - Wₓ = 0
fr = F1 - Wₓ
Let's use trigonometry to find the components of the weight
sin θ = Wₓ / W
cos θ = W_{y} / W
Wₓ = W sin θ
W_{y} = W cos θ
We substitute
fr = F1 - W sin θ
Work is defined by
W = F .dx
W = F dx cos θ
The friction force is parallel to the plane in the negative direction and the displacement is positive along the plane, so the Angle is 180º and the cos θ= -1
W = -fr x
W = (F1 - mg sin θ) L
Another way to calculate is
fr = μ N
fr = μ W cos θ
the work is
W = -μ mg cos θ L
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a) For 0 compressions:
potential energy = U = 0 J
kinetic energy = k = 0.383 J
total mechanical energy = E = 0.383 J
b) For compression of 1 cm:
potential energy = U = 0.0228 J
kinetic energy = k = 0.155 J
total mechanical energy = E = 0.383 J
c) For compression of 2 cm :
potential energy = U = 0.1104 J
kinetic energy = k = 0.272 J
total mechanical energy = E = 0.383 J
d) For compression of 3cm:
potential energy = U = 0.248 J
kinetic energy = k = 0.177 J
total mechanical energy = E = 0.383 J
<h3>Method for solving:</h3>The equations for kinetic energy is:
k= 1/2*m*
The equation for elastic potential energy is:
U= 1/2*ks*
Where,
m= mass of the block
v= velocity
ks= spring constant
x= displacement of the spring
(a)when compression= 0 cm
U= 1/2*ks*
U= 1/2*552*
= 0 J
Kinetic energy:
k= 1/2*m*
k= 1/2*(1.05)*
k= 0.383 J
Mechanical energy:
E= k + U
E= 0.383+0
E= 0.383 J
There will be no work done by friction or any other dissipative force, hence this energy will be conserved, or it will remain constant (like air resistance). This indicates that only spring potential energy will be created from the kinetic energy (there is no thermal energy due to friction, for example).
(b) spring potential = ?
U= 1/2* 457 N/m*
U= 0.0228 J
Since the mechanical energy must remain constant, we may calculate the kinetic energy using the mechanical energy equation:
E= k + U
0.383= k + 0.0228
k= 0.383 - 0.228
k= 0.155
(c)spring constant when x= 0.02
U= 1/2*552*
U= 0.1104 J
Using the equation of mechanical energy:
E= k +U
0.383= k+ 0.1104
k= 0.383 - 0.1104
k= 0.272 J
(d) U= 1/2*552*
U= 0.2484 J
E= 0.383 J
k = E - U
k= 0.383- 0.206
k= 0.177
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