Lower Secondary Science

[tutor76]

Something to let budding tutor outside try it haha

http://i61.tinypic.com/2s9f51s.jpg\">

[tutor76]

Something to let budding tutor outside try it haha

http://i61.tinypic.com/2s9f51s.jpg\">

[spicy]

Hi

I'm a stranger to Physics :scratchhead: , do appreciate help with this question pl. Thanks :please:

http://i60.tinypic.com/xp90k3.jpg\">

[sunnymoon]

Can someone help me with this question?

A basket is being carried by a boy at a constant height above the ground. Is work being done?
Thanks for your help

[superkiasume]

Hi, can someone help my son with the following questions:


(a) The engine of a car of mass 800kg can develop a constant 80kW of power. If its maximum speed on a flat road is 100km/h, determine the resistance to its motion.

(b) With the engine working at the same rate, find the acceleration of the car when is travelling at a speed of 50km/h, if the resistance is constant.

Thank you.

[tutor76]

spicy:

Hi

I'm a stranger to Physics :scratchhead: , do appreciate help with this question pl. Thanks :please:

http://i60.tinypic.com/xp90k3.jpg\">

Charge in coulomb = current x time
Curremt in xy is a series circuit (using conventional current flow )

Therefore current = volt/resistance

Current =1.2ampere

Therefore q=it


Therefore 12v/

1.3333x 10^-19 seconds


I is current 1.2a

Time is charge divide by current =


Formule ,voltage = work done /charge

8v x 1.6x10^-19 coulomb


1.28x 10^-19 J

[tutor76]

[quote="superkiasume"]Hi, can someone help my son with the following questions:


(a) The engine of a car of mass 800kg can develop a constant 80kW of power. If its maximum speed on a flat road is 100km/h, determine the resistance to its motion.

(b) With the engine working at the same rate, find the acceleration of the car when is travelling at a speed of 50km/h, if the resistance is constant.

Thank you.[/quo
There is too many assumption to be made in these two question,is the teacher trying so much to impress the principal with these question ?

Quite unsolvable …

[tutor76]

45has:

http://i60.tinypic.com/23sjh95.jpg\">


1. Calculate current flowing through XY.
2. Calculate voltage across XY.
3. Calculate work done.

I used Kirchoff law to calculate current faster.

Secondary school does not require kirchoff law ,from my experience teaching secondary student science .cheers

[tutor76]

http://i60.tinypic.com/2zg5eo0.jpg\"> Something for everyone to try !

[Dr.033430Daniel]

superkiasume:

Hi, can someone help my son with the following questions:


(a) The engine of a car of mass 800kg can develop a constant 80kW of power. If its maximum speed on a flat road is 100km/h, determine the resistance to its motion.

(b) With the engine working at the same rate, find the acceleration of the car when is travelling at a speed of 50km/h, if the resistance is constant.

Thank you.

For Part a, you can use the formula that at constant velocity

Power = Force X velocity

100km/hr converts to 27.8 m/s

80,000 W = Force X 27.8m/s

So Force = 2880 Newtons.

The driving force pushing the car forward is equal to the force of friction because it is moving at constant velocity.

Usually students remember that Power = Energy / time
At constant velocity the work done to push the car is the force times the distance. Then if we divide by time we get power. So if the car travels 27.8 meters in one second, then force X 27.8m is the work - then divide by 1 second of time. So this is equivalent to saying that Power = Force X velocity when moving at constant velocity.

part (b) is a bit confusing to me. If the engine is working at the same rate, that means it is delivering the same power. But the statement that the resistance is constant is confusing. Most of the resistance to a car is air resistance which depends on speed. So it is a bit hard to decipher part (b).