Which of the following statements is true?
1 answer:
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Average acceleration of the baseball:
Explanation:
Since the motion of the baseball is a uniformly accelerated motion, we can use the following suvat equation:
where
u is the initial velocity
v is the final velocity
a is the acceleration
s is the displacement of the object
For the baseball in this problem, we have:
u = 2.2 m/s is the initial velocity
v = 0 is the final velocity (it comes to a stop)
s = 24 mm = 0.024 m is the displacement of the ball while decelerating
Therefore, we can solve for a to find the acceleration:
where the negative sign means the baseball is slowing down.
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a) The impulse is 76.5 Ns
b) The average force is 546.4 N
c) The final speed is 31.5 m/s
Explanation:
a)
The impulse exerted on an object is defined as
where
F is the magnitude of the force exerted on the object
is the time interval during which the force is applied
If we consider a graph of the force applied vs time, it follows that the impulse exerted is equal to the area under the graph.
Therefore, in this problem, we can calculate the impulse by computing the area under the graph. We have a trapezium, whose bases are
and whose height is
Therefore, the area (and the impulse) is
b)
In this problem, the force applied is not constant. However, we can rewrite the impulse also as
where
is the average force exerted during the whole time
In this problem we have
J = 76.5 Ns is the impulse (calculated in part a)
is the time interval
Solving for the average force, we find
c)
According to the impulse theorem, the impulse exerted on an object is equal to the change in momentum of the object:
where
m is the mass of the object
v is the final velocity
u is the initial velocity
In this problem, we have
J = 76.5 Ns
m = 3.0 kg is the mass
u = 6.0 m/s is the initial velocity
Solving for v, we find the final velocity (and speed):
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at the lowest point in the trajector, the kinetic energy of the bob is 300 J.
Explanation:
The total mechanical energy of the bob at any point of its motion is given by
Where
is the kinetic energy, where
m is the mass of the bob
v is its speed
is the gravitational potential energy, where
g is the acceleration of gravity
h is the height of the bob, measured with respect to the lowest point of the trajector
In absence of friction, the total mechanical energy E remains constant. So we have:
- When the bob swings upward, the PE increases (because h increases) and the KE decreases (so the speed decreases). At the highest point in the trajector, the speed of the bob is zero (v=0), so its KE is also zero and all the mechanical energy is potential energy: U = 300 J
- When the bob swings downward, the PE decreases (because h decreases) and the KE increases (so the speed increases). At the lowest point in the trajectory, the height has become zero (h=0), so the PE is zero and all the mechanical energy is kinetic energy: KE = 300 J
Therefore, at the lowest point in the trajector, the kinetic energy of the bob is 300 J.
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