# IB DP Physics Unit 1. Measurements and uncertainties Paper 1

### Question

Which quantity has the same units as those for energy stored per unit volume?

A Density

B Force

C Momentum

D Pressure

Answer/Explanation

Ans: D

$$\frac{Energy}{Volume}=\frac{work}{area\times length}=\frac{force \times distance}{area\times length}$$

$$=\frac{MLT^{-2}\times L}{L^2\times L}=\left [ ML^{-1}T^{-2} \right ]=pressure$$

### Question

Which is a unit of force?

A. J m

B. J mâ€“1

C. J m sâ€“1

D. J mâ€“1 s

Answer/Explanation

### Markscheme

B

A joule per meter (J/m) is a metric unit of force. In mechanics, a joule is defined as the work done by a force of one newton acting to move an object through a distance of one meter in the direction in which the force is applied (1 J = 1 NÂ·m). Therefore, joule per meter is equal to newton.

### Question

What is the best estimate for the diameter of a helium nucleus?

A. 10â€“21 m

B. 10â€“18 m

C. 10â€“15 m

D. 10â€“10 m

Answer/Explanation

Markscheme

### C

The size of the helium nucleus is about 1 fermi, or 1 fm, which is equivalent to 10-15 m. The atom is about 100,000 times bigger than the nucleus, with an atom size of about 105 fm or 10-10 m.

### Question

How many significant figures are there in the number 0.0450?

A. 2

B. 3

C. 4

D. 5

Answer/Explanation

Markscheme

B

The first one being that all non-zero numbers are significant. With aÂ 4Â and aÂ 5Â in the number, we know there are at leastÂ 2Â significant digits.

Lastly , is that a trailing zero after a decimal is significant. So the 450 is significant. TheÂ  zeros in front of the decimal are irrelevant.

Therefore, there are 3 significant digits in this number. Please visit below link for more details

IB Physics Unit 1. Measurements and uncertainties- 1.1 Measurements in physics: Study Notes

### Question

What is a correct value for the charge on an electron?

A. 1.60Â x 10â€“12 Î¼C

B. 1.60Â x 10â€“15 mC

C. 1.60Â x 10â€“22 kC

D. 1.60Â x 10â€“24 MC

Answer/Explanation

### C

electron, lightest stableÂ subatomic particleÂ known. It carries a negative charge of 1.602176634 Ã— 10âˆ’19Â coulomb, which is considered the basic unit ofÂ electric charge. The rest mass of the electron is 9.1093837015 Ã— 10âˆ’31Â kg, which is onlyÂ 1/1,836the mass of aÂ proton.Â

### Question

What is the unit of electrical energy in fundamental SI units?

A. Â kg m2 Câ€“1 s
B. Â kg m sâ€“2
C. Â kg m2 sâ€“2
D. Â kg m2 sâ€“1 A

Answer/Explanation

### C

Joule is SI unit of work or energy
As work = force x distance
= (mass x acceleration) x distance

$$work=mass \times\frac{distance}{(time)^2}\times distance$$

$$=\frac{mass\times (distance)^2}{time^2}$$

Hence J = $$\frac{kgm^2}{s^2}=kgm^2s^{-2}$$