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sineoko [7]
3 years ago
11

If the work put into a lever is 930 joules and the work accomplished is 870 joules, the efficiency of the lever is _____.

Physics
2 answers:
77julia77 [94]3 years ago
5 0
♥ C) 94%
♥ If the work put into a lever is 930 joules and the work accomplished is 870 joules, the efficiency of the lever is 94%.
♥ <span>870/930=93.5
</span>♥ And rounded you get 94.
Dmitriy789 [7]3 years ago
4 0

The correct answer to this question is C) 94%.

CALCULATION:

As per the question, the work put into a lever is 930 Joule.

Hence, input work W = 930 Joule.

Work accomplished by the lever is 870 Joule.

Hence, the output work W' = 870 Joule.

We are asked to calculate the efficiency of the level.

The efficiency of the lever is defined as the ratio of output work to the input work.

Mathematically efficiency \eta=\ \frac{W'}{W}

                                                =\ \frac{870\ J}{930\ J}

                                                 =\ 0.935

       In percentage, efficiency =\ 0.935\times 100

                                                 =\ 93,5\%

                                                 =\ 94\%                   [ans]

Hence, the efficiency of the lever is 94%.

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8 0
2 years ago
Betty weighs 400 N and she is sitting on a playground swing seat that hangs 0.21 m above the ground. Tom pulls the swing back an
disa [49]

Answer:

4.15 m/s

Explanation:

As the total energy must be conserved (neglecting air resistance) the change in gravitational potential energy, must be equal to the change in kinetic energy:

ΔE = ΔK + ΔU =0

If we take as a zero reference level for the gravitational potential energy, the height of the swing seat above the ground, (which is equal to 0.21 m), we can find the initial gravitational energy, considering the height of the point where the seat is released, regarding this point:

h₀ = 1.09 m -0.21 m = 0.88 m

⇒ U₀ = m*g*h₀ = 400 N*0.88 m = 352 J

As Uf = 0, ΔU = Uf -U₀ = -352 J

As the swing starts from rest, K₀=0, so we can say:

ΔK = Kf = \frac{1}{2} *m*vf^{2}  (1)

As ΔK = -ΔU ⇒ ΔK = 352 J (2)

From (1) and (2) we can solve for vf, as follows:

vf = \sqrt{\frac{2*352J}{40.8kg}} = 4.15 m/s

So, when the swing passes through its lowest position, Betty moves at 4.15 m/s.

5 0
3 years ago
What must the diver's minimum speed be just as she leaves the top of the cliff so that she will miss the ledge at the bottom, wh
Dafna1 [17]

Answer:

1.08 m/s

Explanation:

This can be solved with two steps, first we need to find the time taken to fall 9.5 m, then we can divide the horizontal distance covered with time taken to calculate the velocity.

Time taken to fall 9.5 m

vertical acceleration = a = 9.8 m/s^2.

vertical velocity = 0, (since there is only horizontal component for velocity, )

distance traveled  s = 9.5 m.

Substituting these values in the equation

s= u \timest+0.5at^{2}

t= \sqrt{\frac{2s}{g} }

t=\sqrt{\frac{2\times9.5}{9.8} }

⇒ t= 1.392 sec

Velocity needed

We know the time taken (1.392 s) to travel 1.5 m,

So velocity = 1.5 m / 1.392 s = 1.08 m/s

hence velocity of the diver must be at least 1.08 m/s

4 0
3 years ago
Is the strange solid/liquid changing behavior of Oobleck the SAME as an ice cube melting?
Dmitrij [34]
I don’t think so because an ice cube melting needs heat and relies on temp while ooblecks transition from solid to quickly depends on force and speed
6 0
2 years ago
The speed of a boat in still water is 20 mph. it travels from one pier to another with the current in 4 hours and back against t
saw5 [17]
The answer is, "the speed of the current is 5 miles per hour."

To calculate the speed of the current,
let's assume speed of current =  xmph. Time taken to travel from one pier to another with the current = 100/(20+x)h


But the time taken to travel from one pier to another with the current, which is given is = 4 hours. So,  4=100/(20+x) 80+4x = 100

4x = 20

x = 5 Thus, the speed of the current is 5 miles per hour.
3 0
3 years ago
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