if you drop a softball from just above your knee, the kinetic energy of the ball just before it hits the ground is about 1 jule,
1 answer:
False.
The mass of a softball is approximately 200 g (0.2 kg), while the knees are located approximately at 30 cm (0.3 m) from the ground. It means that the gravitational potential energy of the ball when it is dropped is
This corresponds to the total mechanical energy of the ball at the moment it is dropped, because there is no kinetic energy (the ball starts from rest). Then the ball is dropped, and just before it hits the ground, all this energy is converted into kinetic energy: but energy cannot be created, so its final kinetic energy cannot be greater than 0.6 J.
The mass of a softball is approximately 200 g (0.2 kg), while the knees are located approximately at 30 cm (0.3 m) from the ground. It means that the gravitational potential energy of the ball when it is dropped is
This corresponds to the total mechanical energy of the ball at the moment it is dropped, because there is no kinetic energy (the ball starts from rest). Then the ball is dropped, and just before it hits the ground, all this energy is converted into kinetic energy: but energy cannot be created, so its final kinetic energy cannot be greater than 0.6 J.
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A) The total energy of the system is sum of kinetic energy and elastic potential energy:
where
m is the mass
v is the speed
k is the spring constant
x is the elongation/compression of the spring
The total energy is conserved, so we can calculate its value at any point of the motion. If we take the point of maximum displacement:
then the velocity of the system is zero, so the total energy is just potential energy, and it is equal to
b) When the position of the object is
the potential energy of the system is
and so the kinetic energy is
since the mass is
, and the kinetic energy is given by
we can re-arrange the formula to find the speed of the object:
c) The potential energy when the object is at
is
Therefore the kinetic energy is
d) We already found the potential energy at point c, and it is given by
where
m is the mass
v is the speed
k is the spring constant
x is the elongation/compression of the spring
The total energy is conserved, so we can calculate its value at any point of the motion. If we take the point of maximum displacement:
then the velocity of the system is zero, so the total energy is just potential energy, and it is equal to
b) When the position of the object is
the potential energy of the system is
and so the kinetic energy is
since the mass is
we can re-arrange the formula to find the speed of the object:
c) The potential energy when the object is at
is
Therefore the kinetic energy is
d) We already found the potential energy at point c, and it is given by