Lower Secondary Science

[Verysuperkiasu]

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DS requests me to put this up

In order to know which direction the air bubble move along the capillary tube, he needs to know the water concentration in a carrot tissue. Or do u have any suggested answer?

[Dr.033430Daniel]

Verysuperkiasu:

What's the water concentration level in a typical carrot tissue?

Less than distilled water.

So the distilled water moves into the carrot tissue by osmosis.

[Verysuperkiasu]

Dr.Daniel:

Verysuperkiasu:

What's the water concentration level in a typical carrot tissue?

Less than distilled water.

So the distilled water moves into the carrot tissue by osmosis.

Got it...thanx!

[Gems]

Anyone can help?


1. Pressure exerted by a force of 5N the tip of a knife is 360kPa. What is the area of the tip of knife in cm2?

2.A car moves along a smooth road with its engine exerting a constant force. What change will occur to the car?
a. Its speed will increase.
b. Its acceleration will increase.
c. Its mass will increase.
d. Its direction of movement will change.

Thank you.

[Dr.033430Daniel]

Gems:

Anyone can help?


1. Pressure exerted by a force of 5N the tip of a knife is 360kPa. What is the area of the tip of knife in cm2?

Pressure = Force/Area
Pascals = N/square meter
360,000 Pa = 5N/Area
Area = 1.39 X 10-5 square meters X 10,000 square cm per square meter
= 0.139 cm2

[Dr.033430Daniel]

Gems:

Anyone can help?


2.A car moves along a smooth road with its engine exerting a constant force. What change will occur to the car?
a. Its speed will increase.
b. Its acceleration will increase.
c. Its mass will increase.
d. Its direction of movement will change.

A is the best choice, although there are issues with the question.

\"smooth road\" I interpret as meaning no friction . Usually \"smooth\" means no friction, while \"rough\" indicates friction.

The only possible interpretation of the question given the MCQ choices is that there is a constant driving force and no friction. So that being the case there will be constant acceleration and an increase in speed.

But there is a problem with the question. It is friction between the wheels and the road that allows the driving force to move the car forward. (standard O-Level question by the way). If a car has its wheels on an oil slick and there is no friction, the wheels cannot grab onto the road. The wheels will just turn and there will be no driving force behind the car.

Also, the main contribution to friction opposing the motion in the case of a car is friction with the air.

So a clearer question would be \"a block is pushed on a smooth surface by a constant force.......\"

no issue with wheels, and air friction is minimal just pushing a block along a surface (low speed implied compared to a car)

[Gems]

Sorry, we still don’t understand the 1st question. How to derive at 1.39? Multiply out could not get the area too. Thanks.

[Verysuperkiasu]

Hope to get an answer by today…


Viruses can be classified on the basis of _______
I. Nucleic acid type
II. Nature of host
III. Capsid symmetry
IV. Presence or absence of an envelope

(a) I and II only
(b) III and IV only
I, II and III only
(d) All of the above

Answer is (d). Why? I, II and II ds can understand. But (IV) - he wants to know what the envelope is referring to. If it’s referring to nuclei, then it’s wrong because all viruses have no nucleus.

[Dr.033430Daniel]

An envelope on a virus is on the exterior. The outermost layer on some viruses. It is made up of material from the host cell membrane. Some viruses like influenza use this strategy, but other viruses do not have an envelope. So it can be used as a way of classifying a virus.

[Dr.033430Daniel]

Gems:

Sorry, we still don't understand the 1st question. How to derive at 1.39? Multiply out could not get the area too. Thanks.

360,000 Pa = 5N/Area

Area = 5N/360,000Pa = 1.39 X 10-5 square meters

Pa is N/m2

there are 100 cm in 1 meter, but 10000 cm2 in a m2. So to convert to cm2 multiply by 10,000 to get 0.139 cm2.