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andrew-mc [135]

2 years ago

9

Engineers who design battery-operated devices such as cell phones and MP3 players try to make them as efficient as possible. An

engineer tests a cell phone and finds that the batteries supply 10,000 J of energy to make 5500 J of output energy in the form of sound and light for the screen. How efficient is the phone?

1 answer:

Svetradugi [14.3K]2 years ago

5 0

efficiency= [useful energy transferred ÷ total energy supply]×100%

So, [5500÷10000]×100%=0.55×100

=55%

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A 6000 kg lorry is reversing into a parking space at a speed of 0.5 m/s but collides with a car. The crumple zone of the car sto

zysi [14]

Answer:

3000 kg.m/s

Explanation:

Momentum, p is a product of mass and velocity hence

p=mv where m is mass and v is velocity.

Change in momentum is given by $m(v_f-v_i)$ where subscripts f and i represent final and initial respectively. Since the lorry finally comes to rest then the final velocity is zero. Substituting the given figures then

Change in momentum= 6000(0-0.5)=-3000 kg.m/s

7 0

2 years ago

A car drives 16 miles south and then 12 miles west. What is the magnitude of the car’s displacement? 4 miles 16 miles 20 miles 2

Ostrovityanka [42]

For this case, what we can do is use the Pythagorean theorem to find the magnitude of the displacement of the car.
We have then
$d ^ 2 = 16 ^ 2 + 12 ^ 2
$
From here, we clear the value of d.
We have then:
$d = \sqrt{16 ^ 2 + 12 ^ 2} 
$
Rewriting:
$d = \sqrt{256 + 144}$
$d = \sqrt{400}$
$d = 20 miles
$
Answer:
The magnitude of the car's displacement is:
d = 20 miles

7 0

2 years ago

Read 2 more answers

A professor's office door is 0.99 m wide, 2.2 m high, 4.2 cm thick; has a mass of 27 kg, and pivots on frictionless hinges. A "d

ANEK [815]

Answer:

$I=8.8209\ kg.m^2$

$\alpha=0.6348\ rad.s^{-2}$

Explanation:

Given:

width of door, $w=0.99\ m$

height of the door, $h=2.2\ m$

thickness of the door, $t=4.2\ cm$

mass of the door, $m=27\ kg$

torque on the door, $\tau=5.6\ N.m$

<em>∵Since the thickness of the door is very less as compared to its other dimensions, therefore we treat it as a rectangular sheet.</em>

For a rectangular sheet we have the mass moment of inertia inertia as:

$I=\frac{1}{3} m.w^2$

$I=\frac{1}{3}\times 27\times 0.99^2$

$I=8.8209\ kg.m^2$

We have a relation between mass moment of inertia, torque and angular acceleration as:

$\alpha=\frac{\tau}{I}$

$\alpha=\frac{5.6}{8.8209}$

$\alpha=0.6348\ rad.s^{-2}$

6 0

2 years ago

A planar loop consisting of four turns of wire, each of which encloses 200 cm2, is oriented perpendicularly to a magnetic field

spayn [35]

Answer:

0.6A

Explanation:

Area of loop =200cm2 =200 x10 ∧-4m∧2 Change in Magnetic field (B)= 25mT -10mT =15mT time =5ms

From Faraday' s law of induction EMF(E)= change in magnetic field/time

E= 15mT/5ms

Note, that one weber per second is equivalent to one volt.

= 3V

from Ohm's law I =E/R

=3/5 =0.6A

7 0

2 years ago

Two large parallel conducting plates carrying opposite charges of equal magnitude are separated by 2.20 cm. Part A If the surfac

alukav5142 [94]

Answer:

5308.34 N/C

Explanation:

Given:

Surface density of each plate (σ) = 47.0 nC/m² = $47\times 10^{-9}\ C/m^2$

Separation between the plates (d) = 2.20 cm

We know, from Gauss law for a thin sheet of plate that, the electric field at a point near the sheet of surface density 'σ' is given as:

$E=\dfrac{\sigma}{2\epsilon_0}$

Now, as the plates are oppositely charged, so the electric field in the region between the plates will be in same direction and thus their magnitudes gets added up. Therefore,

$E_{between}=E+E=2E=\frac{2\sigma}{2\epsilon_0}=\frac{\sigma}{\epsilon_0}$

Now, plug in $47\times 10^{-9}\ C/m^2$ for 'σ' and $8.85\times 10^{-12}\ F/m$ for $\epsilon_0$ and solve for the electric field. This gives,

$E_{between}=\frac{47\times 10^{-9}\ C/m^2}{8.854\times 10^{-12}\ F/m}\\\\E_{between}= 5308.34\ N/C$

Therefore, the electric field between the plates has a magnitude of 5308.34 N/C

5 0

2 years ago