2 simple questions and a not-so-simple question (1 Viewer)

[VenomP]

1. How do you determine the frequency of a mechanical wave from a graph?

The graph has amplitude (cm) on the vertical axis and time (seconds) on the horizontal axis.


2. An electrical appliance draws 1.8A from a power source of 240V. How long will it take the electrical appliance to use 20kJ? Answer is 46 seconds


3. A 1500kg vehicle travelling 3m/s West collides with a 1200kg vehicle travelling 7m/s East.

The vehicles lock together. The collision takes 0.12 seconds to occur. Determine the average force of the 1200kg vehicle on the 1500kg vehicle.
Answer: 56,000 N East

Thanks for the help, guys.

 

[Forbidden.]

1. How do you determine the frequency of a mechanical wave from a graph?

The graph has amplitude (cm) on the vertical axis and time (seconds) on the horizontal axis.


2. An electrical appliance draws 1.8A from a power source of 240V. How long will it take the electrical appliance to use 20kJ? Answer is 46 seconds


3. A 1500kg vehicle travelling 3m/s West collides with a 1200kg vehicle travelling 7m/s East.

The vehicles lock together. The collision takes 0.12 seconds to occur. Determine the average force of the 1200kg vehicle on the 1500kg vehicle.
Answer: 56,000 N East

Thanks for the help, guys.

omg i dont have a decent calculator with me here so im restricted to q2.

Power = Current x Voltage = 1.8 x 240 = 432

Power is defined as the rate of change of energy over time i.e.

P = E/t

t = E / P = 20,000 / 432 = 46 seconds

as for q1,
frequency is inverse of period.
so find the period by finding when the graph travels one cycle ... e.g. look at sin x ... its period is 2pi because when you trace out the graph your line should go through "one cycle" at 2pi

Rock On

 

[Shedow]

For Q3, take east at positive

Total initial momentum = 7*1200 - 3*1500 = 3900 (positive, so towards the east)
Therefore, as momentum is conserved, final momentum = initial momentum = 3900 Ns east

Final velocity of 1500kg cart = final velocity of stuck carts = v = p/m = 3900/(1500+1200) = 1.44 m/s

Initial velocity of 1500kg cart = p/m = -4500/1500 = -3 m/s

Therefore, delta v = change in velocity = 4.44 m/s

So, as Ft = delta p = m*(delta v)
So F = 1500*4.44/0.12 = 56000 N (2 s.f.)

 

[VenomP]

For Q3, take east at positive

Total initial momentum = 7*1200 - 3*1500 = 3900 (positive, so towards the east)
Therefore, as momentum is conserved, final momentum = initial momentum = 3900 Ns east

Final velocity of 1500kg cart = final velocity of stuck carts = v = p/m = 3900/(1500+1200) = 1.44 m/s

Initial velocity of 1500kg cart = p/m = -4500/1500 = -3 m/s

Therefore, delta v = change in velocity = 4.44 m/s

So, as Ft = delta p = m*(delta v)
So F = 1500*4.44/0.12 = 56000 N (2 s.f.)

For the bolded part, why do we need to know delta V?

What is delta P? Change in momentum?

Impulse = force x time = Change in momentum...right?

(Almost understand )

 

[clonestar]

1. How do you determine the frequency of a mechanical wave from a graph?

The graph has amplitude (cm) on the vertical axis and time (seconds) on the horizontal axis.


2. An electrical appliance draws 1.8A from a power source of 240V. How long will it take the electrical appliance to use 20kJ? Answer is 46 seconds


3. A 1500kg vehicle travelling 3m/s West collides with a 1200kg vehicle travelling 7m/s East.

The vehicles lock together. The collision takes 0.12 seconds to occur. Determine the average force of the 1200kg vehicle on the 1500kg vehicle.
Answer: 56,000 N East

Thanks for the help, guys.

I'll have a jab at these.

For No 1 the wave - the time base represents an important relationship with f=1/T where T= period (i.e. the time in seconds) for one complete wavelength. When this is known(just take 2 crests or two troughts or one complete wavelngth period) just sub it in from the graph and voila frequency is now obtained. Just make sure you get your units in.

For No 2
You should have been taught P=W/t Power = Work/time and then re-arrange work = power x time. You should also know twinkle twinkle little star power consumed = I squared R so therefore

W=P x time
W = I^2 R x t

Now using ohms law R=V/I and put in data R= 240/1.8 = 133.3 ohms

Now use this in above formula
W= I^2Rt
20000 = 1.8^2 x 133.3 ohms x t
Make t the subject
t= 46.2secs

For No3
Coalesce collision indicates the two come together

so therefore impulse = change in momentum
Ft= mv-mu

therefore F=mv-mu/t
Now remember here you want the v and u for the 1500kg mass so you are gonna have to go back to inelastic coalesce collision formula

i.e m1u1 + m2u2 = (m1 + m2) V
and work out V

Here V = 1.4m/s East

Now go back to original F=mv-mu/t
sub in

= 1500(+1.4) - 1500(-3)/0.12

therefore f= 55555.6N(east) as + = East
or 5.6 x 10^4 N (East)


Hope this clarifies it better.
Enjoy.
:jaw: