A construction crane lowers a beam into place at constant speed. Consider the work Wg done by gravity on the beam and the work W
1 answer:
Answer:
Wg is positive and WT negative.
(Letters in options are all wrongly written).
Explanation:
Remember that the work of a force is the internal product between the force and the displacement .
Since the displacement is downwards like the weight, the work done by gravity is positive, while the work done by the tension is negative since it points upwards.
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Answer:
Explanation:
The first thing to have to make a diagram where we indicate the forces acting on the block, see attached. We have the following
The weight (W) that is vertical
The friction force (fr) that opposes the movement
The driving force (F)
The normal (N) which is the reaction to the support of the body and is perpendicular to the surface
We write a reference system where one axis is parallel to the surface (x axis) and the other is perpendicular to it (Y axis) we decompose the forces on these axes, we see that the only force we have to decompose r is the weight
sin θ = Wx / W ⇒ Wx = W sin θ
cos θ = Xy / W ⇒ Wy = Wcos θ
We write Newton's equations for each axis
N- Wy = 0
F -fr -Wx = m a (1)
The expression for the friction force is
fr = μ N
N = Wy
N = W cos θ
fr = μ mg cosT
We hope, we simplify the acceleration of equation 1
a = F - μ mg cos θ -mg sinθ
a = F - mg (μ cos θ -sin θ)
This is the general equation for movement.
