Physics Questions & Answers - Free Online Practice

2,756.

4g of a radioactive material of half-life 10 days is spilled on a laboratory floor. How long would it take to disintegrate 3.5g of the material?

1\(\frac{1}{4}\) days

8\(\frac{1}{4}\) days

30 days

80 days

View answer & explanation

Correct answer is C

half-life = 10 days

after 10 days, the 4g of element = 2g remaining with 2g disintegrated

after 10 days, 2g of element = 1g left with 1g disintegrated

hence, after 20 days, 3g of the element has been disintegrated with 1g left.

after 10 days, the 1g of element = 0.5g left with 0.5g disintegrated

after 30 days, we have 0.5g of element left with 3.5g disintegrated.

2,757.

When an atom loses or gains a charge, it becomes

an electron

an ion

a neutron

a proton

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

2,758.

Which of the following statements are TRUE of isotopes?

i. isotopes of an element have the same chemical properties because they have the same number of electrons.
ii. isotopes of elements are normally separated using physical properties.
iii. isotopes of an element have the same number of protons in their nuclei.

i and ii only

i and iii only

ii and iii only

i, ii, and iii

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

2,759.

The electrochemical equivalent of platinum is 5.0 x 10^-7kgC^-1 to plate-out 1.0kg of platinum, a current of 100A must be passed through an appropriate vessel for

5.6 hours

56 hours

1.4 x 10^{4 hours}