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3 years ago

If we know the total energy in a system is 30 J, and we know the PE is 20 J. What is the KE?

Physics

1 answer:

svetoff [14.1K]3 years ago

3 0

Can you give more description ??

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A railroad car of mass 2.50*10^4 kg is moving with a speed of 4.00 m/s. It collides and couples with three other coupled railroa

NemiM [27]

Answer:

(a) 2.5 m/s

(b) 37.5 KJ

Explanation:

(a)

From the law of conservation of momentum, Initial momentum=Final momentum

$mV_1+3mV_2=(m+3m)V_f=4mV_f$

$V_1+3V_2=4V_f$ and making $V_f$ the subject then

$V_f=\frac {V_1+3V_2}{4}$ and since $V_1$ is initial velocity of car, value given as 4 m/s, $V_2$ is the initial velocity of the three cars stuck together, value given as 2 m/s and $v_f$ is the final velocity which is unknown. By substitution

$V_f=\frac {4+(3\times2)}{4}=2.5 m/s$

(b)

Initial kinetic energy is given by

$\frac {mV_1^{2}}{2}+\frac {3mV_2^{2}}{2}=\frac {m(V_1^{2}+3V_2^{2}}{2}=\frac {2.5\times 10^{4}(4^{2}+3(2^{2}))}{2}=350\times10^{3} J= 350 KJ$

Final kinetic energy is given by

$\frac {4mV_f^{2}}{2}=\frac {4\times 2.5\times 10^{4}\times 2.5^{2}}{2}=312.5\times 10^{3} J=312.5 KJ$

The energy lost is given by subtracting the final kinetic energy from the initial kinetic energy hence

Energy lost=350-312.5=37.5 KJ

6 0

3 years ago

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It takes 5.0 seconds for a wave with a wavelength of 2.5 m to travel past your location. What’s the period of the wave. What is

Anna35 [415]

(a) Period of the wave
The period of a wave is the time needed for a complete cycle of the wave to pass through a certain point.
So, if an entire cycle of the wave passes through the given location in 5.0 seconds, this means that the period is equal to 5.0 s: T=5.0 s.

(b) Frequency of the wave
The frequency of a wave is defined as
$f= \frac{1}{T}$
since in our problem the period is $T=5.0 s$ , the frequency is
$f= \frac{1}{5.0 s}=0.2 Hz$

(c) Speed of the wave
The speed of a wave is given by the following relationship between frequency f and wavelength $\lambda$ :
$v=f \lambda = (0.2 Hz)(2.5 m)=0.5 m/s$

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The correct answer is D, Diamond

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