Aspeaker fixed to a moving platform moves toward a wall, emitting a steady sound with a frequency of 225 hz . a person on the platform right next to the speaker detects the sound waves reflected off the wall and those emitted by the speaker. part a how fast should the platform move, vp, for the person to detect a beat frequency of 7.00 hz ? take the speed of sound to be 344 m/s. express your answer

Polly is pushing a box across the floor with a force of 30 n. the force of gravity is –8 n, and the normal force is 8 n. which value could describe the force of friction if polly could not move the box?

If you wanted to move an electron from the positive to the negative terminal of the battery, how much work w would you need to do on the electron? enter your answer numerically in joules.

Refrigerant-134a flows through a carnot heat pump cycle at 0.5 kg/s. it is known that the maximum absolute temperature in the cycle is 1.1 times the minimum absolute temperature, and the net power input to the cycle is 2.5 kw. if the refrigerant changes from a saturated vapor to a saturated liquid during the heat rejection process, determine the maximum magnitude of the enthalpy of vaporization for this process in kj/kg (with 3 significant figures).