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VMariaS [17]
3 years ago
14

A skier weighing 86.2 kg starts from rest and slides down a 32.0-m frictionless slope that is inclined at an angle of 15.0° with

the horizontal. Ignore air resistance.
a. calculate the work done by gravity on the skier.

b.calculate the work done by the normal force on the skier

Physics
1 answer:
Mashcka [7]3 years ago
5 0

Answer:

A. = 26.11kJ

B = 0N

Explanation:

Mass = 86.2kg

Distance (s) = 32m

Angle of the slope = 15°

a. Work done due to gravity

W = force * distance * angle of displacement

W = F * S * cos θ

Force = mass * acceleration due to gravity

Force = 86.2 * 9.8

Force = 844.76N

Work = 844.76 * 32 * cos 15

Work = 26111.21J

Work = 26.11kJ

b. The workdone by the normal force is equal to zero since the normal force is perpendicular to the displacement.

Hence the normal force does not act on the body.

N = 0N

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Answer:

1) f= 8.6 GHz

2) t= 0.2 ms

Explanation:

1)

  • Since microwaves are electromagnetic waves, they move at the same speed as the light in vacuum, i.e. 3*10⁸ m/s.
  • There exists a fixed relationship between the frequency (f) , the wavelength (λ) and the propagation speed in any wave, as follows:

        v = \lambda * f (1)

  • Replacing by the givens, and solving for f, we get:

       f =\frac{c}{\lambda} =\frac{3e8m/s}{0.035m} = 8.57e9 Hz (2)

⇒     f = 8.6 Ghz (with two significative figures)

2)

  • Assuming that the microwaves travel at a constant speed in a straight line (behaving like rays) , we can apply the definition of average velocity, as follows:

       v =\frac{d}{t} (3)

       where v= c= speed of light in vacuum = 3*10⁸ m/s

       d= distance between mountaintops = 52 km = 52*10³ m

  • Solving for t, we get:

       t = \frac{d}{c} = \frac{52e3m}{3e8m/s} = 17.3e-5 sec = 0.173e-3 sec = 0.173 ms (4)

       ⇒  t = 0.2 ms (with two significative figures)

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Answer:

the correct answer is b: 25

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A 300W hot plate produces 45,000 J of thermal energy while operating for 2 min. What is the efficiency of this devide? it need t
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Answer:

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t_1 = \frac{d}{v_1}

t_1 = \frac{d}{45}

now the same distance is traveled by him with speed 55 mph

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