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son4ous [18]
3 years ago
11

Estimate the power you produce in running up a flight of stairs. Give your answer in horsepower (1 hp = 746 W). Suppose you clim

b one flight of stairs (3 m) in 10 seconds (you run up the stairs quickly). Estimate your mass to be 71 kg .
Physics
2 answers:
Andrej [43]3 years ago
5 0
<span>If we call the time it took for you to climb the stairs in seconds, T, the height of the stairs in meters, h, your weight in newtons, W, then to find the power you developed in watts, P, the following formula restates what we said above: Power = W x h/t, W= 71kg x 9.81m/sec sq.= 696.51 N, Height h= 3m, time t= 10 sec, Power P=( 696.51 x3) 10= 208.953 watts = 0.28 hp.</span>
GarryVolchara [31]3 years ago
3 0
The first thing you should do is calculate the work done when climbing the stairs. This work by definition will be given by:
 W = F * d
 W = (m * g) * (d)
 W = ((71) * (9.8)) * (3) = 2087.4J
 Then, you can calculate the power that in this case is given by
 P = W / t
 P = (2087.4) / (10) = 208.74W
 To have the result in HP we use the fact that 1HP = 746W
 P = (208.74) / (746)
 P = 0.28 HP
 answer
 the power you produce in running up a flight of stairs is 0.28 HP
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There is a missing data in the text of the problem (found on internet):
"with force constant<span> k=</span>450N/<span>m"

a) the maximum speed of the glider

The total mechanical energy of the mass-spring system is constant, and it is given by the sum of the potential and kinetic energy:
</span>E=U+K=  \frac{1}{2}kx^2 + \frac{1}{2} mv^2
<span>where
k is the spring constant
x is the displacement of the glider with respect to the spring equilibrium position
m is the glider mass
v is the speed of the glider at position x

When the glider crosses the equilibrium position, x=0 and the potential energy is zero, so the mechanical energy is just kinetic energy and the speed of the glider is maximum:
</span>E=K_{max} =  \frac{1}{2}mv_{max}^2
<span>Vice-versa, when the glider is at maximum displacement (x=A, where A is the amplitude of the motion), its speed is zero (v=0), therefore the kinetic energy is zero and the mechanical energy is just potential energy:
</span>E=U_{max}= \frac{1}{2}k A^2
<span>
Since the mechanical energy must be conserved, we can write
</span>\frac{1}{2}mv_{max}^2 =  \frac{1}{2}kA^2
<span>from which we find the maximum speed
</span>v_{max}= \sqrt{ \frac{kA^2}{m} }= \sqrt{ \frac{(450 N/m)(0.040 m)^2}{0.500 kg} }=  1.2 m/s
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b) </span><span> the </span>speed<span> of the </span>glider<span> when it is at x= -0.015</span><span>m

We can still use the conservation of energy to solve this part. 
The total mechanical energy is:
</span>E=K_{max}=  \frac{1}{2}mv_{max}^2= 0.36 J
<span>
At x=-0.015 m, there are both potential and kinetic energy. The potential energy is
</span>U= \frac{1}{2}kx^2 =  \frac{1}{2}(450 N/m)(-0.015 m)^2=0.05 J
<span>And since 
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<span>we find the kinetic energy when the glider is at this position:
</span>K=E-U=0.36 J - 0.05 J = 0.31 J
<span>And then we can find the corresponding velocity:
</span>K= \frac{1}{2}mv^2
v=  \sqrt{ \frac{2K}{m} }= \sqrt{ \frac{2 \cdot 0.31 J}{0.500 kg} }=1.11 m/s
<span>
c) </span><span>the magnitude of the maximum acceleration of the glider;
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For a simple harmonic motion, the magnitude of the maximum acceleration is given by
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\omega =  \sqrt{ \frac{450 N/m}{0.500 kg} }=30 rad/s
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a_{max} = \omega^2 A = (30 rad/s)^2 (0.040 m) =36 m/s^2

d) <span>the </span>acceleration<span> of the </span>glider<span> at x= -0.015</span><span>m

For a simple harmonic motion, the acceleration is given by
</span>a(t)=\omega^2 x(t)
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e) </span><span>the total mechanical energy of the glider at any point in its motion. </span><span>

we have already calculated it at point b), and it is given by
</span>E=K_{max}= \frac{1}{2}mv_{max}^2= 0.36 J
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