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2 years ago

Efficiency of a machine is always less than 100% why?

Physics

1 answer:

kifflom [539]2 years ago

7 0

The reason the efficiency is always less than 100% is because there is always some sort of friction in the machine.

Answer: because of friction

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A cord is used to vertically lower an initially stationary block of mass M = 3.6 kg at a constant downward acceleration of g/7.

dalvyx [7]

Answer:

(a) $W_c=127.008 J$

(b) $W_g=148.176 J$

(c) K.E. = 21.168 J

(d) $v=3.4293m.s^{-1}$

Explanation:

Given:

mass of a block, M = 3.6 kg

initial velocity of the block, $u=0 m.s^{-1}$

constant downward acceleration, $a_d= \frac{g}{7}$

$\Rightarrow$ That a constant upward acceleration of $\frac{6g}{7}$ is applied in the presence of gravity.

∴ $a=- \frac{6g}{7}$

height through which the block falls, d = 4.2 m

(a)

Force by the cord on the block,

$F_c= M\times a$

$F_c=3.6\times (-6)\times\frac{9.8}{7}$

$F_c=-30.24 N$

∴Work by the cord on the block,

$W_c= F_c\times d$

$W_c= -30.24\times 4.2$

We take -ve sign because the direction of force and the displacement are opposite to each other.

$W_c=-127.008 J$

(b)

Force on the block due to gravity:

$F_g= M.g$

∵the gravity is naturally a constant and we cannot change it

$F_g=3.6\times 9.8$

$F_g=35.28 N$

∴Work by the gravity on the block,

$W_g=F_g\times d$

$W_g=35.28\times 4.2$

$W_g=148.176 J$

(c)

Kinetic energy of the block will be equal to the net work done i.e. sum of the two works.

mathematically:

$K.E.= W_g+W_c$

$K.E.=148.176-127.008$

K.E. = 21.168 J

(d)

From the equation of motion:

$v^2=u^2+2a_d\times d$

putting the respective values:

$v=\sqrt{0^2+2\times \frac{9.8}{7}\times 4.2 }$

$v=3.4293m.s^{-1}$ is the speed when the block has fallen 4.2 meters.

6 0

3 years ago

Which group of measurements is the most precise? A) 2 g, 3 g, 4 g B) 2 g, 2.5 g, 3 g C) 2.0 g, 3.0 g, 4.0 g, 5.0 g D) 2.0 g, 3.0

siniylev [52]

The answer to your question is A

3 0

3 years ago

Which statement explains the similarity between momentum and kinetic energy of an object?

Anon25 [30]

Answer:B.

Both increase as the mass and velocity increase.

3 0

3 years ago

Read 2 more answers

A CD player uses 1200 J of energy in 60 seconds what is the power rating of the CD player

tiny-mole [99]

The power equals energy divided by the time

P=E/t

P=1200/60

P=20W

Hope you get it!

8 0

3 years ago

If someone ways 600 newtons and the shoes have an area of 300cm squared, what pressure does he exert on the ground?

lukranit [14]

Pressure = Force / Area

Put your data in front of yourself.

Force = 600 Newtons
Area = 300 cm^2

Firstly you need to convert the area into m^2 and you do this by diving 300 with 10000.

Now you use the formula:-
Pressure = 600/ 0.03
Which comes out to be 20,000 Pa.

Hope this helps!

4 0

3 years ago