The tower crane is used to hoist a 2.0mg- load upward at constant velocity. The 1.7Mg- jib BD and 0.6-Mg jib BC have centers of
mass at G1 and G2, respectively.
Determine the required mass of the counterweight C so that the resultant moment produced by the load and the weight of the tower crane jibs about point A is zero.
The center of mass for the counterweight is located at G3.
Determine the required mass of the counterweight C so that the resultant moment produced by the load and the weight of the tower crane jibs about point A is zero.
The center of mass for the counterweight is located at G3.
1 answer:
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Answer:
a) The work done by the applied force is 1500 joules.
b) The kinetic energy of the block after 10 seconds is 1200 joules.
c) The magnitude of the force of friction is 3 newtons and its direction is against motion.
d) 300 joules of energy are lost during motion.
Explanation:
a) Since the object has a constant mass, on which a constant horizontal force is exerted. The work done by the force (), measured in joules, is defined by the following expression:
(1)
Where:
- Force, measured in newtons.
- Distance, measured in meters.
If we know that and
, then the work done by the force exerted on the object is:
The work done by the applied force is 1500 joules.
b) At first we need to calculate the net acceleration of the object (), measured in meters per square second. By assuming a constant acceleration, we use the following kinematic formula:
(2)
Where is the initial velocity of the object, measured in meters per second.
We clear the acceleration within the equation above:
If we know that ,
and
, then the net acceleration experimented by the object is:
By the 2nd Newton's Law, we construct the following equation of equilibrium under the consideration of a friction force acting against the motion of the object:
(3)
Where:
- External force exerted on the object, measured in newtons.
- Kinetic friction force, measured in newtons.
If we know that ,
and
, the kinetic friction force is:
The work done by friction (), measured in joules, is:
(4)
And the net work experimented by the object is:
By the Work-Energy Theorem we understand that change in translational kinetic energy (), measured in joules, is equal to the change in net work. That is:
(5)
If we know that , then the change in translational kinetic energy is:
The kinetic energy of the block after 10 seconds is 1200 joules.
c) The magnitude of the force of friction is 3 newtons and its direction is against motion.
d) The energy lost by the object is equal to the work done by the force of friction. Therefore, 300 joules of energy are lost during motion.