When you lift a book from the ground to your desk, what kind of work do you do, negative or positive? By lifting the book, what do you change? Does the book gain or lose energy? What kind of energy?


Answer 1
Answer: Ascencion means gain in potential energy and descing is the opposite, hence when you lift a book, you apply a positive work."
"You lose energy where as book gains energy. Therefore, positive work on book, negative on you."

Answer 2
Answer: Your doing positive work and the energy is called potential energy 

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Which physical properties of nylon and leather make them good choices for shoelaces?



Flexibility and durability.


The material of leather and nylon is durable which means it can be used for a long period of time and the material is also flexible means it is not hard. The material which is used in shoe laces can be chosen on the basis of its flexibility and its long lasting nature because costumer do not want to invest on them more than one time or on the basis of easily use.

Therefore, due to the long lasting nature means durability and their flexibility nylon and leather is mostly used in shoe laces.

durability and flexibility

look at you shoelaces they are not hard, don't move like a liquid, or have a high density.


An elevator is accelerating upward at a rate of 3.6 m/s2. a block of mass 24 kg hangs by a low-mass rope from the ceiling, and another block of mass 90 kg hangs by a low-mass rope from the upper block. (a) what are the tensions in the upper and lower ropes?


The answer:

When the elevator accelerates upward at a rate of 3.6 m/s², the value of the acceleration becomes

A=g+3.6=13.4 m/s²
and by using the newton's law, F=mass x A, we have 
T1= (24 + 90 )x 13.4= 1527.6 N, where T1 is the Tension in upper rope
T2= ( 90 )x 13.4= 1206N, where T2 is the Tension in lower rope

When the elevator accelerates downward at a rate of 3.6 m/s², the value of the acceleration becomes
A=9.8 - 3.6 = 6.2 m/s²

T1= (24 + 90 )x 6.2= 706.8 N, where T1 is the Tension in upper rope
T2= ( 90 )x 6.2= 558N, where T2 is the Tension in lower rope


A boat heads due North for 3.00 km to reach a red buoy. It then changes direction and heads in a direction of 30.0 degrees South of East for a distance of 4.66 km to reach a blue buoy. The boat changes direction again and heads to a green buoy which is 1.00 km due East of the boat’s starting position. What must be the boat’s displacement to go from the blue buoy to the green buoy? Express that displacement as the distance travelled in a direction specified as an angle East or West of South.


Position of B :  

x = 4.66*cos 30 = 4.036  

y = 3-4.66*sin 30 = 3-2.33 = 0.67  

BC = √y^2+(x-1)^2 = √0.67^2+3.036^2 = 3.109  

heading = arctan y/(x-1) = arctan 0.67/(3.036) = 12.44° south of west

hope this helps :)


Batteries should only be removed from the premises by a licensed battery hauler for recycling. A) True B) False





Batteries carry acids and electrolytes which if comes in contact with human skin can cause severe effects and sometimes it can become fatal. Therefore a great care is needed while replacing batteries. To avoid any danger and harmful circumstances, batteries should always be replaced by a licenced battery haulers for recycling.

Its true you !!!!!!!!!!!!!!!!!!!!!!1

A cannonball is launched horizontally off a 80 m high castle wall with a speed of 25 m/s. How long will the cannonball be in flight before striking the ground



The cannonball will be spend 4.04 seconds before striking the ground.



vertical height = 80 m

horizontal velocity = 25m/s

Initial vertical velocity, Vy= 0

Applying equations of motion;

s = Vy*t + ¹/₂gt²

80 = ¹/₂*9.8t²

4.9t² = 80

t² = 80/4.9

t² = 16.327

Therefore, the cannonball will be spend 4.04 seconds before striking the ground.


2.23 s.



S = 80 m

voy = 0 m/s

vox = 25 m/s

g = 9.81 m/s^2

Using equation of motion,

S = vo*t + 1/2 * g * t^2

80 = 0 + 4.905t^2

Solving this equation, we have:

t = sqrt(16.31)

= 4.039 s

Therefore, t = 4.04 s.


A soccer player kicks a soccer ball initially at rest setting it in motion at a velocity of 30 m/s. If the ball has a mass of 0.50 kg and the time of contact is 0.025 s, what is the force exerted on the player’s foot?



 F= 600 N


Given that

Initial velocity ,u= 0 m/s

Final velocity ,v= 30 m/s

mass ,m = 0.5 kg

time ,t= 0.025 s

The change in the linear momentum is given as

ΔP= m (v - u)

ΔP= 0.5 ( 30 - 0 ) kg.m/s

ΔP= 15 kg.m/s

We know that from second law of Newtons

Now by putting the values

F= 600 N


While some aspects are based on ____, body composition is largely a result of ____, A. BMI;BMR

B. Diet;Excercise

C. Heredity;Lifestyle

D. Lifestyle;Heredity


Answer : Option C) Heredity; Lifestyle.

Explanation : While some aspects are based on heredity, body composition is largely a result of Lifestyle.

Even though it is believed that 80 percent of the aspects of a human body is heredity, but an individual body composition is largely influenced by the result of the lifestyle an individual lives.


C) Heredity; Lifestyle




In a football game, a defensive lineman exerts a force upon an offensive lineman, causing the offensive lineman to be accelerated backward at 2 m/s2. If the offensive lineman's mass were doubled, how much force would the defensive lineman have to apply to accelerate the offensive lineman 2 m/s2 backward? A. half as much B. twice as much C. four times as much D. the same amount


Defensive holding (5 yards (4.57 m), automatic first down). This penalty is frequently assessed to defensive backs who stop a receiver from moving forward. Thus, option B is correct.

What apply to accelerate the offensive lineman?

An object's acceleration is directly inversely proportional to its mass and directly inversely proportional to the force being applied to it.

Offensive linemen who are on the line of scrimmage and in the zone at the snap may continue to block in the back against defensive players.  If the contact is made in the zone and both players are in the zone at the time.

Therefore, In this scenario, doubling the mass of the offensive lineman would require doubling the force applied to him in order to achieve the same acceleration (2 m/s2).

Learn more about offensive lineman here:



The answer is B (twice as much)


The magnitude, or amount, of an object's acceleration is directly proportional to the magnitude of the force exerted upon it and inversely proportional to its own mass.

In this case, if the offensive lineman's mass were doubled, then the force exerted upon him would also have to be doubled to produce the same acceleration (2 m/s2).


A child rides her bike at a rate of 12.0 km/hr down the street. A squirrel suddenly runs in front of her so she applies the brakes and slows to 8.0 km/hr in 0.25 sec. What is the acceleration of the bike rider during this period?


By v = u - at 
=>8 = 12 - a x 0.25 
=>a = 4/0.25 km/hr/sec 
=>a = 16km/hr/sec

I hope this helped!

it should be 16 kilometers per second

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