Science Review (4.1) 17Jul

X, Y and Z are three regions of different temperatures.

Which object is the hottest?

• X

• Y

• Z

Answer explanation

Heat flows from hot to cold region. If heat flow from X to Y, X is hotter than Y. Since Y is hotter than Z and X is hotter than Y, X is the hottest.

X, Y and Z are three regions of different temperatures.

Which region is the coldest?

• X

• Y

• Z

• surrounding

Answer explanation

Heat travel from hot to cold regon. Since heat from X, Y and Z all flow to the surrounding, surrounding is the coldest region.

Energy cannot be created but can be destroyed.

• True

• False

Answer explanation

Energy cannot be created and cannot be destroyed. It can be converted to other forms or transferred to another body.

A machine does 5000 J of work in 10 seconds. What is its power?

Answer explanation

P = E/t = 5000 / 10 = 500 W

A toaster has a power of 200 W. It is turned on for 1 minute.

How much energy is given out by the toaster?

Answer explanation

E = P x t

= 200 W x 60 s

= 12000J

To use this formula, the time must be in seconds. Hence we must convert 1 minute to 60 s.

10 waves pass through a point in 5 seconds.

What is the frequency of the wave?

Answer explanation

Frequency = no. of waves produced in 1 s

Since 10 waves pass through a point in 5 s, it means that 10 waves are produced in 5 s.

10/5 = 2 Hz

It means that 2 waves are produced in 1 second.

What is the amplitude of this wave?

• 2 cm

• 4 cm

• -2 cm

Answer explanation

Amplitude is the distance between the highest point (crest) to the centre line.

or the lowest point (trough) to the centre line.

The presence of starch can be tested with _______

The presence of protein can be tested with ............... solution

When iodine is added to a food sample, a yellowish brown is observed.

When biuret solution is added to the sample, it turns purple.

Which nutrient is present?

• starch only

• protein only

• starch and protein

• protein adn fat

Answer explanation

If starch is present, iodine will turn from yellowish brown to blue black.

If protein is present, it will turn from blue to purple.