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Lelu [443]
3 years ago
14

A cyclist starts from rest and coasts down a 4.0∘ hill. The mass of the cyclist plus bicycle is 85 kg. Ignore air resistance and

friction.
A) After the cyclist has traveled 180 m , what was the net work done by gravity on the cyclist?

B) How fast is the cyclist going? in m/s

please explain if possible!!
Physics
1 answer:
Angelina_Jolie [31]3 years ago
5 0

A) change in ht after 180m = 180 * sin(4-deg.) = 12.56m

net work done by gravity on the cyclist = mass * gravity * height diff.

= 85 * 9.8 * 12.56

= 10470J

= 10.5kJ

B) Kinetic energy = 1/2 * mass * vel.^2 = work done by gravity = 10470J

vel.^2 = 10470 * 2 / 85 = 246.4

vel. = 15.7m/s

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A proton moves from a location where V = 87 V to a spot where V = -40 V. (a) What is the change in the proton's kinetic energy?
Art [367]

Answer: a) 127 eV; b) there is no change of kinetic energy.

Explanation: In order to explain this problem we have to use the change of potentail energy ( conservative field) is equal to changes in kinetic energy. So for the proton ther move to lower potential then they gain kinetic energy from the electric field.  This means the electric force do work in this trayectory and then the protons increased changes its speed.

If we replace the proton by a electron we have a very different situaction, the electrons are located in a lower potental then  they can not move to higher potential  if any  external force does work on the system.

In resumem, the electrons do not move from a point with V=87 to other point with V=-40 V. The electric force point to high potential so the electrons  can not move to lower potential region (V=-40V).

6 0
4 years ago
A student drops an object out the window of the top floor of a high-rise dormitory.
seropon [69]

-- The acceleration due to gravity is 32.2 ft/sec² .  That  means that the
speed of a falling object increases by an additional 32.2 ft/sec every second.

-- If dropped from "rest" (zero initial speed), then after falling for 4 seconds,
the object's speed is (4.0) x (32.2) = <em>128.8 ft/sec</em>.

-- 128.8 ft/sec = <em>87.8 miles per hour</em>

Now we can switch over to the metric system, where the acceleration
due to gravity is typically rounded to 9.8 meters/sec² .

-- Distance = (1/2) x (acceleration) x (time)²

       D = (1/2) (9.8) x (4)² =<em>  78.4 meters</em>

-- At 32 floors per 100 meters,  78.4 meters = dropped from the <em>25th floor</em>.


The 5 points are certainly appreciated, but I do wish they were Celsius points.


3 0
3 years ago
Someone please help me
schepotkina [342]
The answer is oil and water. If you want I could give you the reason too
5 0
3 years ago
Read 2 more answers
A wire of length 5mm and Diameter 2m extends by 0.25 when a force of 50N was use. calculate the
bazaltina [42]

Answer and Explanation:

Data provided in the question

Force = 50N

Length = 5mm

diameter = 2.0m = 2\times 10^{-3}

Extended by = 0.25mm = 0.25\times 10^{-3}

Based on the above information, the calculation is as follows

a. The Stress of the wire is

= \frac{force\ applied}{area\ of \ circle}

here area of circle = perpendicular to the are i.e cross-sectional  i.e

= \frac{\pi d^{2}}{4}

= \frac{\pi(2\times 10^{-3})^2}{4}

Now place these above values to the above formula

= \frac{4\times 50}{\pi\times 4 \times 10^{-6}} \\\\ = \frac{50}{\pi}

= 15.92 MPa

As 1Pa = 1 by N m^2

So,

MPa = 10^6 N m^2

b. Now the strain of the wire is

= \frac{Change\ in\ length}{initial\ length} \\\\ = \frac{0.25\times 10^{-3}}{5}

= 5 \times 10^{-5}

3 0
4 years ago
Richard Julius once made a model plane that could travel a max speed of 110 m/s. Suppose the plane was held in a circular path b
hjlf

Answer:

85.8 m/s

Explanation:

We know that the length of the circular path, L the plane travels is

L = rθ where r = radius of path and θ = angle covered

Now,its speed , v = dL/dt = drθ/dt = rdθ/dt + θdr/dt

where dθ/dt = ω = angular speed = v'/r where v' = maximum speed of plane and r = radius of circular path

Now, from θ = θ₀ + ωt where θ₀ = 0 rad, ω = angular speed  and t = time,

θ = θ₀ + ωt = 0 + ωt = ωt

So, v = rdθ/dt + θdr/dt

v = rω + ωtdr/dt

v = (r + tdr/dt)ω

v = (r + tdr/dt)v'/r

v = v' + tv'/r(dr/dt)

v = v'[1 + t(dr/dt)/r]

Given that v' = 110 m/s, t = 33.0s, r = 120 m and dr/dt = rate at which line is shortened = -0.80 m/s (negative since it is decreasing)

So, v = 110 m/s[1 + 33.0 s(-0.80 m/s)/120 m]

v = 110 m/s[1 + 11.0 s(-0.80 m/s)/40 m]

v = 110 m/s[1 + 11.0 s(-0.02/s)]

v = 110 m/s[1 - 0.22]

v = 110 m/s(0.78)

v = 85.8 m/s

8 0
3 years ago
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