A stone is thrown vertically upward with a speed of 18 m/s. (a) How long does it take the stone to reach a height of 11 m? (b) h
ow fast is the stone traveling? (c) how many possible answers are there and why? what would the 3 Kinematic graph look like. thanks
1 answer:
Answer:
a) It takes the stone 0.7743 s to reach a height of 11 m for the first time on its way up and 2.899 s to reach again that height on its way down.
b) At t = 0.7743 s the velocity is 10.41 m/s and at t = 2.899 s the velocity is -10.41 m/s.
c) There are two answers because the stone reaches the height of 11 m one time on its way up and one more time again on its way down.
Please, see the attached figures and the explanation for a description of the figures.
Explanation:
Hi there!
The equations for the height and velocity of the stone are as follows:
y = y0 + v0 · t + 1/2 · g · t²
v = v0 + g · t
Where:
y = height
y0 = initial height
v0 = initial velocity
t = time
g = acceleration due to gravity (-9.8 m/s² considering the upward direction as positive)
v = velocity at time t
a) Let´s calculate the time it takes the stone to reach a height of 11 m. The origin of the frame of reference is at the throwing point so that y0 = 0:
y = y0 + v0 · t + 1/2 · g · t²
11 m = 18 m/s · t - 1/2 · 9.8 m/s² · t²
0 = -4.9 m/s² · t² + 18 m/s · t - 11 m
Solving the quadratic equation:
t = 0.7743 s and t = 2.899 s
(Notice that I have used more significant figures to avoid error by rounding)
The stone will be two times at a height of 11 m, one on its way up (at 0.7743 s) and one on its way down (at 2.899 s). Then, it takes the stone 0.7743 s to reach a height of 11 m for the first time.
b) Let´s use the equation of velocity:
v = v0 + g · t
at t = 0.77443 s
v = 18 m/s - 9.8 m/s² · 0.77443 s
v = 10.41 m/s
at t = 2.899 s
v = 18 m/s - 9.8 m/s² · 2.899 s
v = - 10.41 m/s
(Both velocities have to be of the same magnitude but of different sign, that´s why I haven´t rounded the time.)
c) There are two answers because the stone reaches the height of 11 m one time on its way up and one more time again on its way down. On its way up, the velocity is 10.41 m/s and on its way down it is -10.41 m/s.
Figures
The functions to plot are the following:
height in function of time (figure 1, x-axis: time. y-axis: height)
y = -4.9t² + 18t
velocity in function of time (figure 2, x-axis: time. y-axis velocity)
v = -9.8t + 18
Acceleration in function of time (figure 3, x-axis: time. y-axis: acceleration)
a = -9.8
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Answer:
a. It starts at point B.
vp = 2.53*10⁴ m/s
a. it starts at point A.
ve= 1.08*10⁶ m/s
Explanation:
a) As the proton is a positive charge, when released from rest, it will be accelerated due to the potential difference, from the higher potential to the lower one, so it is at the point B when released.
Once released, as the total energy must be conserved, the increase in kinetic energy must be equal (in magnitude) to the change in the electric potential energy, as follows:
ΔK + ΔUe = 0 ⇒ ΔK = -ΔUe =- (e*ΔV)
⇒
where e= elementary charge= 1.6*10⁻¹⁹ C, VA = 1.83 V, VB= 5.17V, and mp= mass of proton = 1.67*10⁻²⁷ kg.
Replacing by these values, and solving for v, we have:
⇒ vp = 2.53*10⁴ m/s
b) If, instead of a proton, the charge realeased from rest, had been an electron, a few things would change:
First, as the electrons carry negative charges, they move from the lower potentials to the higher ones, which means that it would have started at point A.
Second, as its charge is (-e) the change in electric potential energy had been negative also:
ΔUe = -e*ΔV = -e* (VB-VA)
In order to find the speed of the electron when it is just passing point B, we can apply the conservation of energy principle as for the proton, as follows:
where e= elementary charge= 1.6*10⁻¹⁹ C, VA = 1.83 V, VB= 5.17V, and me= mass of electron = 9.1*10⁻³¹ kg.
Replacing by these values, and solving for v, we have:
⇒ ve = 1.08*10⁶ m/s
Answer:
v = 1.15*10^{7} m/s
Explanation:
given data:
charge/ unit area
plate seperation = 1.69*10^{-2} m
we know that
electric field btwn the plates is
force acting on charge is F = q E
Work done by charge q id
this work done is converted into kinectic enerrgy
solving for v
v = 1.15*10^{7} m/s