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Physics Work,E,P
Physics Spring Y12
| Question | Answer |
|---|---|
| What is work done | Literally just say work done = force x displacement in the direction of the force |
| Orbit work done | F towards body. Velocity always forwards perpendicular so work done is zero for any distance so speed of orbiting body is constant. Force can change in direction so can accelerate but not speed. |
| Where energy going when pushing at constant speed | Thermal energy - balanced against friction |
| Derivation of mgh | Consider mass m lifted through height h. No kinetic energy increase if it starts and ends at rest, so work = Fh, so Ep = mgh |
| Derivation of Ke | W = Fs Ek = Fs F = ma Ek = mas v^2 = u^2 + 2as. If it starts at rest v^2 = 2as Sub in |
| how much energy someone has by top of loop | Work out potential energy gained but look at previous parts of Q to also add how much Ke he has |
| For a motor circuit efficiency experiment | Draw a circuit diagram as well as the normal one. Remember to measure mass. |
| Why gravitational potential of weight decreases more than elastic potential increases (also weight oscillated a bit after sinking before equilibrium). Also state the energy changes. | GPE → EPE + KE (when falling) EPE → GPE + KE (when rising) Some energy dissipated as heat as oscillates (because of air resistance / friction) |
| A ball is thrown at an angle of 30° to the horizontal. The initial kinetic energy of the ball is K. Air resistance has negligible effect on the motion of the ball. Find the kinetic energy at its highest point in terms of K | Can't split energy into components. The component for velocity horizontally is v(cos30). Kinetic energy = 1/2 * m * v^2 Horizontal energy = 1/2 * m * (vcos30)^2 = 1/2 mv^2 (cos30)^2 = 0.75K |
| Circle with 2 rockets on it facing the same direction spinning. Work done amount | Work is still done by the rotating thing. 2 sources of the force so double the work done. |
| Why train stops slower when travelling up slope | Some K energy transferred to GPE *so* it stops slowe as there is greater FORCE acting against movement so decelerates more |
| If constant force causes an acceleration | Have to say CONSTANT acceleration |
| Efficiency of motor | Not just total - effective as GPE Also remove the P = I^2 x R |
| W = Fd equation can only be used when? | When there is constant force. For a car braking, we don't know that |
| How to work out power dissipated by brakes of car when braking? | Change in KE/time |
| Power supplied to motor to lift weight of 4N through vertical height of 0.9m in 1.8s. 20% motor efficiency | Way more power to meet the requirements of lifting. 10W |
| Sand falling onto mass balance | Work out the force of the sane landing (change in momentum over change in time), turn that into a mass reading, and add to the final mass |
| Uncertainty when y = 0.400 | It's to 3d.p. so use that |
| Explain the term systematic error | Deviates by a fixed amount from the true value of a measurement |
| Masses changed on outer sides of 2 pulleys with mass hung between the pulleys. What is the effect on the height of the middle mass? | Friction opposing increasing mass of outside masses |
| Thrust of rocket relating to final acceleration | Remember to remove W from net force |
| equation for the power required to move an object at a constant velocity against resistive forces | P = W/t = Fx/t = Fv |
| Phrasing efficiency | Useful output/total input |
Created by:
Pyrogearos2