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Brut [27]
3 years ago
13

A student does 25 J of work on the handle of a pencil sharpener. If the pencil sharpener does 20 J of work on the pencil, what i

s the efficiency of the sharpener?
Physics
1 answer:
allsm [11]3 years ago
3 0

Answer:

80%

Explanation:

Efficiency of machine = work output/work input  ×100 %

From question, work output = 20J

Work input = 25J.

Therefore efficiency = 20/25 × 100 %

Efficiency = 20×4 %

Efficiency = 80%

I hope this was helpful, please mark as brainliest

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41. City A lies 30 km directly south of city B. A bus, beginning at city A travels 50 km at 37° north of east to reach city C. H
Nana76 [90]

Answer:

B) 40 km West

Explanation:

Let position of B is origin so with respect of City B the position of A is given as

r_A = 30 km south of city B

now Bus starts from City A and travels a distance of 50 km at 37 degree North of East to reach city C

so it is

r_{CA} = 50(cos37\hat i + sin37 \hat j)

r_{CA} = 40\hat i + 30\hat j

now the position of C is given with respect to A

in order to find the position of C with respect to B we can say

r_C = r_{CA} + r_A

r_C = 40\hat i + 30\hat j + (-30 \hat j)

r_C = 40 \hat i

so in order to reach at city B from city C bus has to travel 40 km towards West

7 0
3 years ago
An electromagnetic wave is transporting energy in the negative y direction. At one point and one instant the magnetic field is i
natali 33 [55]

Answer:. Option c

Explanation: the speed of an electromagnetic wave is simply the vector product of the magnetic field and the electric field.

The direction of the velocity is the direction of the electromagnetic wave.

The wave is already moving towards the negative y axis (-j) and the magnetic field is already pointing towards the positive x axis (i)

From cross product of unit vectors

i × j = k

i × k = - j

With the second identity, we can see that the electric field will be pointing towards the positive of the x axis (k).

Option c is validated

4 0
3 years ago
Red light Green light is used to work on what skill?
Talja [164]
Running for sure ptttt
4 0
3 years ago
Read 2 more answers
An object moving due to gravity can be described by the motion equation y=y0+v0t−12gt2, where t is time, y is the height at tha
LenaWriter [7]

Answer:

t=6.4534 s

Explanation:

This is an exercise where you need to use the concepts of <em>free fall objects</em>

Our <u>knowable variables</u> are initial high, initial velocity and the acceleration due to gravity:

y_{0}=75m

v_{oy} =20m/s

g=9.8 m/s^{2}

At the end of the motion, the <u><em>rock hits the ground</em></u> making the final high y=0m

y=y_{o}+v_{oy}*t-\frac{1}{2}gt^{2}

If we <em>evaluate the equation</em>:

0=75m+(20m/s)t-\frac{1}{2}(9.8m/s^{2})t^{2}

This is a classic form of <u><em>Quadratic Formula</em></u>, we can solve it using:

t=\frac{-b ± \sqrt{b^{2}-4ac } }{2a}

a=-4.9\\b=20\\c=75

t=\frac{-(20) + \sqrt{(20)^{2}-4(-4.9)(75) } }{2(-4.9)}=-2.37s

t=\frac{-(20) - \sqrt{(20)^{2}-4(-4.9)(75) } }{2(-4.9)}=6.4534s

Since the <u><em>time can not be negative</em></u>, the <em>reasonable answer</em> is

t=6.4534s

8 0
3 years ago
An unstretched spring has a length of 10. centimeters. When the spring is stretched by a force of 16 newtons, its length is incr
Alinara [238K]
A) 16N/8cm=2N/cm
;)))
5 0
3 years ago
Read 2 more answers
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