1. L

    Power required to accelerate

    A body of mass m moves up a plane inclined at an angle "theta" to the horizontal. What is the power required by the body for it to have an acceleration "a" when its instantaneous velocity is v? My idea is that the power required = power to overcome the body's weight + power to accelerate...
  2. L

    Expression of power

    Power is defined by P=W/t where W is work done and t is the time. If force F is constant, then power can also be P=Fv where v is the velocity, which sort of can be derived from P=W/t=Fs/t=Fv. Since F=ma, also P=mav..........(1) However, if work done is turned into kinetic energy, E=(1/2)mv^2...
  3. C

    Help calculating power required to lift a mass

    Hello, I realize that this is a Physics 101 pop quiz problem, but it's been 45 years since I was in Physics 101 I'm trying to figure out what size of a 12VDC motor to purchase to perform the following work. I have a 40 Kg tool that I want to lift 30cm within 60 seconds. If you need the length...
  4. A

    Finding optical power of corrective lenses?

    The question is as follows: "A person with presbyopia has a near point of 40 cm. This person wears glasses to correct their vision such that they can comfortably read the screen of their mobile phone when it is held 25 cm from their eyes. If this person wears their glasses such that they sit...
  5. A

    Finding the power used to change phase?

    I have figured the heat added to the system so far, but can't figure out where to go from here to get the change in internal energy to work out the work(W)? https://imgur.com/a/4SiM6fd It is question number 3 right at the bottom of the photo. Thank you for any help.
  6. A

    Rotational Power = torque (τ)*(ω) angular velocity? - Problem with units

    I set up an experiment with a pendulum (uniform beam) swinging on a hinge and the hinge attached to a small PMDC generator. The generator had no load attached and its output voltage is proportional to its speed of rotation. I swung the pendulum from 90 degrees and using a data logger I...
  7. M

    Rotor and power of engine

    The question and answer that I have problem understanding is as follows: A helicopter of mass 800 kg rises to a height of 170 metres in 20 seconds, before setting off in horizontal flight. Calculate the potential energy gain of the helicopter, and hence estimate the mean power of its engine...
  8. R

    Power Calculations

    Hello everybody Could you help me to solve this question ? Best regards Razi
  9. A

    Power of a rotor - derivation

    I'm trying to understand the equation P = 2(pi)TN/60, where T=torque, N=rpm... So far I understand: E = F.d = F.(2.pi.r)*(no. of revolutions) = 2T.pi.n And P = E/t = 2T.pi.n/t - but n/t is revolutions per second, so: P = 2T.pi.f f = rev/second This is where I'm having...
  10. retrodynamic

    How Can Be Described the Formula of the Retrodynamic Effect?

    *Wordpress Blog State of the Art Novel InFlow Gearturbine Imploturbocompressor Retrodynamic Dextrogiro vs Levogiro Phenomenon Effect. / Rotor-RPM VS InFlow / front to front; "Collision-Interaction Type" - inflow vs blades-gear-move. Technical unique dynamic innovative motion mode...
  11. J

    Work, power and rotational motion problem

    Hi Everyone, Happy new year to you all. It's been a wee while since I was on the forum .. been a bit unwell for a few weeks .. but I'm better again. I have a problem that has taxed my understanding of the subject matter in the title, namely work-power and rotational motion. The problem is as...
  12. M

    calculate the temperature due to Power loss over a res.

    Hi All, Having the following problem I am trying to solve I am an electronics guy some of e physics eludes me in my calc. Here goes.... I am supplying 125Vac into a R which is a 20kohm resistor where I have a 12V zener in series to GND. P_loss = (125Vac - 5V)^2 / R P_loss = 0.72W So lets...
  13. S

    how to study

    whenever we study physics numericals,units,definition of quantities in physics and formulas practice should be done to it strong. but my problem is when we study physics i encounter examples in middle of chapter like numericals can i solve numericals when i finish reading chapter.
  14. S

    regarding undrstanding

    i forgot the concepts understanding word by word without practical imaginative thinking. how to understand physics like a story. can anyone can tell me
  15. P

    Energy, work and power question

    I can't work out why I'm getting the part ii wrong and I was wondering if you could help. A mouse of mass 15g is stationary 2m below its hole. It runs to its hole, arriving 1.5 seconds later with a speed of 3ms^-1. i) Show that the acceleration of the mouse it not constant. [Done by using...
  16. L

    Is this Power/Work problem Possible

    I am currently in AP Physics C. I was given a homework problem that I don't think is possible with the given info. A 20 kg rock slides on a rough horizontal surface at 8 m/s and eventually stops due to friction. The coefficient of kinetic friction between the rock and the surface is 0.200...
  17. A

    Power bank, AC adapter and Cell phone Charging

    I want to make a power bank for my cell phone(Li-ion battery: 2070mAh). The AC adapter of the phone has an output rating of 5V dc and 550mA. Now a power bank consists of a dc battery. So it's voltage and current(?) will decrease. Now, I have heard that a battery charges in a few states(i.e...
  18. A

    power consumption

    The question is An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be __________. I proceed with P = VI. I found I (electric current) = 100/220. This I substituted in P = VI. = 110 * (100/220) = 50...
  19. P

    Electromagnet actuator increase power

    Hello All, I am trying to make a device that presses down on a foot pedal when activated. The main requirement is that it needs to be silent and powerful. I have tried other types of actuators and servos, but all are too noisy. My next idea was to use an large electromagnet (salvaged...
  20. B

    Calculate Power Rating of Pump

    Dear all, I am required to determine the power rating of the pump required for a two storey building shown in the attachment. The number of faucets in each storey is 20. I would be grateful if someone could help me solve this. Thanks!