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3 years ago

when a book falls from a shelf to the ground without anyone pushing on it, no work is done to the book. True or False

Physics

1 answer:

VikaD [51]3 years ago

8 0

That's false.

-- The force on the book is its weight.

-- The force acts through the distance the book falls.

-- The work done on the book is

(weight) x (length of the fall)

-- Gravity DOES the work.

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Superman takes 8 seconds to stop a runway train over a distance of 58 m using a power of

elena-14-01-66 [18.8K]

Answer:

Workdone = 600 Kilojoules

Explanation:

Given the following data:

Time = 8 seconds

Power = 75,000 Watts

Distance = 58 m

To find the work done;

Power can be defined as the energy required to do work per unit time.

Mathematically, it is given by the formula;

$Power = \frac {Energy}{time}$

Thus, work done is given by the formula;

Workdone = power * time

Workdone = 75000 * 8

Workdone = 600,000 = 600 KJ

5 0

4 years ago

Name and describe two forces that act on your body as you walk down the hallway.

defon

Gravity & Resistance ?

3 0

4 years ago

(b) The density of aluminum is 2.70 g/cm3. The thickness of a rectangular sheet of aluminum foil varies

vekshin1

Answer:

(i) $22.48 cm^3$

(ii) $1.5 mm$

Explanation:

Let t be the average thickness of the sheet.

Given that:

Density of the aluminum sheet is $2.70 g/cm^3$

Mass of sheet = 60.7 g

Length of sheet = 50.0 cm

Width of sheet = 30.0 cm

(i) Using, Density=Mass/Volume

$\Rightarrow \text{Volume}=\frac{\text{Mass}}{\text{Density}}$

$\Rightarrow \text{Volume}=\frac{60.7}{2.7}=22.48 cm^3$

Hence, the volume of the sheet is $22.48 cm^3$ .

(ii) Now, as this aluminum sheet is in the shape of a cuboid, so the volume of the sheet is

$\text{Volume}=\text{Length}\times\text{Width}\times\text{Thickness}$

$\Rightarrow 22.48=50\times 30 \times w$

$\Rightarrow w=\frac{22.48}{50\times 30}=0.015 cm$

Hence, the average thickness of the sheet is $1.5 mm$ .

6 0

4 years ago

The graph shows a car's velocity over time.

OleMash [197]

Answer:

Explanation:

It starts from 60 and 50

5 0

4 years ago

A 45.0 - kg girl is standing on a 150. - kg plank. The plank, originally at rest, is free to slide on a frozen lake, which is a

Mrac [35]

Answer:

The velocity relative to the surface of the ice is 6.5 m/s.

Explanation:

Given that,

Mass of girl m= 45.0 kg

Mass of plank M= 150 kg

Velocity = 1.50 m/s

We need to calculate the velocity relative to the surface of the ice

Using conservation of momentum

$mv_{1}+Mv_{2}=(m+M)v$

Here, $v_{2}=0$ because plank at rest

$v_{1}=\dfrac{m+M}{m}\times v$

Put the value into the formula

$v_{1}=\dfrac{45+150}{45}\times1.50$

$v_{1}=6.5\ m/s$

Hence, The velocity relative to the surface of the ice is 6.5 m/s.

6 0

3 years ago