Watch
Announcements
#1
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

0
6 years ago
#2
(Original post by 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

period/Time is measured in seconds, s so 1 over s will give you s^-1, which is units for frequency
λ, wavelength is measure in meters, m so m x s^-1 gives you units for speed
1
6 years ago
#3
(Original post by 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

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. 0
#4
(Original post by 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. 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.
0
6 years ago
#5
(Original post by 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.
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. 1
#6
(Original post by 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. I know from GCSE the simple equation
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
0
6 years ago
#7
(Original post by 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
Distance = speed * time only works when acceleration = 0.

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. 0
X

new posts Back
to top
Latest
My Feed

Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Poll

Join the discussion

What is your favourite revision method?

Taking notes manually (77)
21.04%
Note taking apps (6)
1.64%
Flashcards (84)
22.95%
Revision guides (19)
5.19%
Past papers (166)
45.36%
Something else (let us know in the thread) (14)
3.83%