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givi [52]
3 years ago
14

The specialty of an athlete on the women's track team is the pole vault. She has a mass of 48 kg and her approach speed is 8.9 m

/s. When she is directly above the bar, her speed is 1.6 m/s. Neglecting air resistance and any energy absorbed by the pole, determine the amount(in m) she has raised herself as she crosses the bar.
Physics
1 answer:
Lyrx [107]3 years ago
4 0

Answer:

H = 3.9 m

Explanation:

mass (m) = 48 kg

initial velocity (initial speed) (U) = 8.9 m/s

final velocity (V) = 1.6 m/s

acceleration due to gravity (g) = 9.8 m/s^{2}

find the height she raised her self to as she crosses the bar (H)

from energy conservation, the change in kinetic energy = change in potential energy

0.5m(V^{2} - [test]U^{2}[/tex]) = mg(H-h)

where h = initial height = 0 since she was on the ground

the equation becomes

0.5m(V^{2} - [test]U^{2}[/tex]) = mgH

0.5 x 48 x (1.6^{2} - [test]8.9^{2}[/tex]) = 48 x 9.8 x H

-1839.6 = 470.4 H  (the negative sign indicates a decrease in kinetic energy so we would not be making use of it further)

H = 3.9 m

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7.5 meters per second

Explanation:

30 / 4 = 7.5

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A transformer connected to a 120-v(rms) at line is to supply 13,000V(rms) for a neon sign.
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Answer:

(a) 108

(b) 110.500 kW

(c) 920.84 A

Solution:

As per the question:

Voltage at primary, V_{p} = 120\ V          (rms voltage)

Voltage at secondary, V_{s} = 13000\ V  (rms voltage)

Current in the secondary, I_{s} = 8.50\ mA  

Now,

(a) The ratio of secondary to primary turns is given by the relation:

\frac{N_{s}}{N_{p}} = \frac{V_{s}}{V_{s}}

where

N_{p} = No. of turns in primary

N_{s} = No. of turns in secondary

\frac{N_{s}}{N_{p}} = \frac{13000}{120} ≈ 108

(b) The power supplied to the line is given by:

Power, P = V_{s}I_{s} = 13000\times 8.50 = 110.500\ kW

(c) The current rating that the fuse should have is given by:

\frac{V_{s}}{V_{p}} = \frac{I_{p}}{I_{s}}

\frac{13000}{120} = \frac{I_{p}}{8.50}

I_{p} = \frac{13000}{120}\times 8.50 = 920.84\ A

 

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3 years ago
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