# 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

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 m–1

C. J m s–1

D. J m–1 s

### 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 N·m). Therefore, joule per meter is equal to newton.

### Question

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

A. 10–21 m

B. 10–18 m

C. 10–15 m

D. 10–10 m

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

Markscheme

B

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

Lastly , is that a trailing zero after a decimal is significant. So the 450 is significant. The  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. 1.60 x 10–12 μC

B. 1.60 x 10–15 mC

C. 1.60 x 10–22 kC

D. 1.60 x 10–24 MC

### C

electron, lightest stable subatomic particle known. It carries a negative charge of 1.602176634 × 10−19 coulomb, which is considered the basic unit of electric charge. The rest mass of the electron is 9.1093837015 × 10−31 kg, which is only 1/1,836the mass of a proton.

### Question

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

A.  kg m2 C–1 s
B.  kg m s–2
C.  kg m2 s–2
D.  kg m2 s–1 A

### 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 = $$\frac{kgm^2}{s^2}=kgm^2s^{-2}$$