# Struggling to Understand 'Simple Physics' Could anyone please help me

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Sam00

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I am revising for a physics exam and I really don't understand the concept.

Here are the 1st 3 questions I am practicing but don't get:

Q: Using the information below find the units for the following quantities

1: frequency (f) f=1/t

2: Speed of light (c) c= λf

3: Energy of an object due to its mass (E) E=mc^2

Where f, t, c, E and m represent frequency, time, speed of light, energy and mass

I really don't understand this supposedly simple physics concept, could anyone please help?

Here are the 1st 3 questions I am practicing but don't get:

Q: Using the information below find the units for the following quantities

1: frequency (f) f=1/t

2: Speed of light (c) c= λf

3: Energy of an object due to its mass (E) E=mc^2

Where f, t, c, E and m represent frequency, time, speed of light, energy and mass

I really don't understand this supposedly simple physics concept, could anyone please help?

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jonnypdot

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#2

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#2

(Original post by

I am revising for a physics exam and I really don't understand the concept.

Here are the 1st 3 questions I am practicing but don't get:

Q: Using the information below find the units for the following quantities

1: frequency (f) f=1/t

2: Speed of light (c) c= λf

3: Energy of an object due to its mass (E) E=mc^2

Where f, t, c, E and m represent frequency, time, speed of light, energy and mass

I really don't understand this supposedly simple physics concept, could anyone please help?

**Sam00**)I am revising for a physics exam and I really don't understand the concept.

Here are the 1st 3 questions I am practicing but don't get:

Q: Using the information below find the units for the following quantities

1: frequency (f) f=1/t

2: Speed of light (c) c= λf

3: Energy of an object due to its mass (E) E=mc^2

Where f, t, c, E and m represent frequency, time, speed of light, energy and mass

I really don't understand this supposedly simple physics concept, could anyone please help?

λ, wavelength is measure in meters, m so m x s^-1 gives you units for speed

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ombtom

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#3

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#3

**Sam00**)

I am revising for a physics exam and I really don't understand the concept.

Here are the 1st 3 questions I am practicing but don't get:

Q: Using the information below find the units for the following quantities

1: frequency (f) f=1/t

2: Speed of light (c) c= λf

3: Energy of an object due to its mass (E) E=mc^2

Where f, t, c, E and m represent frequency, time, speed of light, energy and mass

I really don't understand this supposedly simple physics concept, could anyone please help?

1: f = 1/t. Unit for t = s (seconds), so unit for f = 1/s = s^-1. This is the same as Hz (hertz).

2: c = λf. Unit for λ = m (metres), unit for f = Hz = s^-1, so unit for c = ms^-1 = m/s (metres per second).

I'll leave the last one for you to try. If you have any problems I'll be happy to help.

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Sam00

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#4

(Original post by

You can replace the symbols with the units.

1: f = 1/t. Unit for t = s (seconds), so unit for f = 1/s = s^-1. This is the same as Hz (hertz).

2: c = λf. Unit for λ = m (metres), unit for f = Hz = s^-1, so unit for c = ms^-1 = m/s (metres per second).

I'll leave the last one for you to try. If you have any problems I'll be happy to help.

**ombtom**)You can replace the symbols with the units.

1: f = 1/t. Unit for t = s (seconds), so unit for f = 1/s = s^-1. This is the same as Hz (hertz).

2: c = λf. Unit for λ = m (metres), unit for f = Hz = s^-1, so unit for c = ms^-1 = m/s (metres per second).

I'll leave the last one for you to try. If you have any problems I'll be happy to help.

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ombtom

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#5

(Original post by

I have the answer in my book, I just don't understand why the answer is what it is. My book says it is km^2 / s^2? I also don't understand your explanations as I don't fathom the concept.

**Sam00**)I have the answer in my book, I just don't understand why the answer is what it is. My book says it is km^2 / s^2? I also don't understand your explanations as I don't fathom the concept.

(I assume you meant that the book says kg*m^2/s^2).

Do you understand how to convert 1/x to x^-1?

If you have an equation, say speed = distance / time, and you know the units for all but one quantity, you can find the unknown units, by substituting in the known units and rearranging. So if you know the units for speed = m/s (=ms^-1), and the units for time = s, then since distance = speed*time, the units for distance = (m/s)*s = m.

Hope this helps.

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Sam00

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#6

(Original post by

Unit for E = kg * (ms^-1)^2 = kg*m^2*s^-2

(I assume you meant that the book says kg*m^2/s^2).

Do you understand how to convert 1/x to x^-1?

If you have an equation, say speed = distance / time, and you know the units for all but one quantity, you can find the unknown units, by substituting in the known units and rearranging. So if you know the units for speed = m/s (=ms^-1), and the units for time = s, then since distance = speed*time, the units for distance = (m/s)*s = m.

Hope this helps.

**ombtom**)Unit for E = kg * (ms^-1)^2 = kg*m^2*s^-2

(I assume you meant that the book says kg*m^2/s^2).

Do you understand how to convert 1/x to x^-1?

If you have an equation, say speed = distance / time, and you know the units for all but one quantity, you can find the unknown units, by substituting in the known units and rearranging. So if you know the units for speed = m/s (=ms^-1), and the units for time = s, then since distance = speed*time, the units for distance = (m/s)*s = m.

Hope this helps.

D

S x T

But this is different for example I have

A hamster in its ball starts at rest and accelerates to 3m/s in 6 seconds.

a) What was the acceleration?- The answer is 0.5ms^2 (Acceleration = v - u / t)b)

b) What was the distance the hamster traveled? I assumed it would be (3 x 6 = 18) but the answer is actually 9m.

This goes against the formula I was taught at GCSE

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ombtom

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#7

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#7

(Original post by

I know from GCSE the simple equation

D

S x T

But this is different for example I have

Ahamster in its ball starts at rest and accelerates to 3m/s in 6 seconds.

a) What was the acceleration?- The answer is 0.5ms^2 (Acceleration = v - u / t)b) What was the distance the hamster traveled. I assumed it would be (3 x 6 = 18) but the answer is actually 9m. This goes against the formula I was taught at GCSE

**Sam00**)I know from GCSE the simple equation

D

S x T

But this is different for example I have

Ahamster in its ball starts at rest and accelerates to 3m/s in 6 seconds.

a) What was the acceleration?- The answer is 0.5ms^2 (Acceleration = v - u / t)b) What was the distance the hamster traveled. I assumed it would be (3 x 6 = 18) but the answer is actually 9m. This goes against the formula I was taught at GCSE

Suvat equations only work when acceleration = constant (so they work when a = 0).

You probably won't come across variable acceleration at AS level, except for in graph form (where calculations will involve area and gradient).

So for your hamster question, you need to use suvat.

s = ?

u = 0

v = 3

a = 0.5

t = 6

v^2 = u^2 + 2as

9 = 2*0.5*s

s = 9/1 = 9m.

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