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bija089 [108]
3 years ago
13

A bicyclist is coasting straight down a hill at a constant speed. The mass of the rider and bicycle is 96.0 kg, and the hill is

inclined at 17.0° with respect to the horizontal. Air resistance opposes the motion of the cyclist. Later, the bicyclist climbs the same hill at the same constant speed. How much force (directed parallel to the hill) must be applied to the bicycle in order for the bicyclist to climb the hill?

Physics
1 answer:
mr_godi [17]3 years ago
5 0

Answer:

 The force applied 275 N in a direction parallel to the hill

Explanation:

Newton's second law is adequate to work this problem, in the annex we can see a free body diagram, where the weight (W) is vertical, the friction force (fr) is parallel to the surface and the normal (N ) is perpendicular to it. In general for these problems a reference system is taken that is parallel to the surface and the Y axis is perpendicular to it.

Let us decompose the weight into its two components, the angle T is taken from the axis and

            Wx = W sin θ

            Wy = W cos T

We write Newton's second law

              ∑ F = m a

X axis

          The cyclist falls at a constant speed, which implies that the acceleration is zero

              fr - W sin θ = 0

              fr = mg sin θ

              fr = 96 9.8 without 17

              fr = 275 N

When the cyclist returns to climb the hill, he must apply the same force he has to overcome the friction force that always opposes the movement .  The force applied 275 N in a direction parallel to the hill

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9. Consider the elbow to be flexed at 90 degrees with the forearm parallel to the ground and the upper arm perpendicular to the
mojhsa [17]

Answer:

Moment about SHOULDER  ∑ τ = 3.17 N / m,

Moment respect to ELBOW   Στ= 2.80 N m

Explanation:

For this exercise we can use Newton's second law relationships for rotational motion

         ∑ τ = I α

   

The moment is requested on the elbow and shoulder at the initial instant, just when the movement begins.

They indicate the angular acceleration, for which we must look for the moments of inertia of the elements involved

The mass of the forearm with the included weight is approximately 2.3 kg, with a length of about 50cm

Moment about SHOULDER

          ∑ τ = I α

           I = I_forearm + I_sphere

the forearm can be approximated as a fixed bar at one end

            I_forearm = ⅓ m L²

the moment of inertia of the mass in the hand, let's approach as punctual

            I_mass = m L²

we substitute

           ∑ τ = (⅓ m L² + M L²) α

let's calculate

          ∑ τ = (⅓ 2.3 0.5² + 0.5 0.5²) 10

           ∑ τ = 3.17 N / m

Moment with respect to ELBOW

In this case, the arm exerts an upward force (muscle) that is about 3 cm from the elbow

         Στ = I α

         I = I_ forearm + I_mass

         I = ⅓ m (L-0.03)² + M (L-0.03)²

         

let's calculate

        i = ⅓ 2.3 0.47² + 0.5 0.47²

        I = 0.2798 Kg m²

        Στ = 0.2798 10

        Στ= 2.80 N m

3 0
3 years ago
which statements about velocity are true? check all that apply. a. for velocity, you must have a number, a unit, and a direction
satela [25.4K]
a). for velocity, you must have a number, a unit, and a direction.
Yes.  This one isn't bad.  The 'number' and the 'unit' are the speed.

b). the si units for velocity are miles per hour.
No.  That's silly. 
'miles' is not an SI unit, and 'miles per hour'
is only a speed, not a velocity. 

c). the symbol for velocity is .
You can use any symbol you want for velocity, as long as
you make its meaning very clear, so that everybody knows
what symbol you're using for velocity.
But this choice-c is still wrong, because either it's incomplete,
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d). to calculate velocity, divide the displacement by time.
Yes, that's OK, but you have to remember that the displacement
has a direction, and so does the velocity.
3 0
3 years ago
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Rainbow [258]

Explanation:

Usually when we think of waves, we think of transverse waves.  These are waves where points move up and down perpendicular to the motion of the wave.  Examples include water waves, whipping a rope, or even doing the "wave" in a crowd.  You can think of these as "two dimensional" waves.

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4 0
3 years ago
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