Shoveling snow can be extremely taxing since the arms have such a low efficiency in this activity. Suppose a person shoveling a sidewalk metabolizes food at the rate of 700 W. (The efficiency of a person shoveling is 3%). (a) What is her useful power output (in W)?(b) How long (in s) will it take her to lift 3,400 kg of snow 1.20 m? (c) How much waste heat (in J) will she generate in the process?

Scientists use laser range-finding to measure the distance to the moon with great accuracy. a brief laser pulse is fired at the moon, then the time interval is measured until the "echo" is seen by a telescope. a laser beam spreads out as it travels because it diffracts through a circular exit as it leaves the laser. in order for the reflected light to be bright enough to detect, the laser spot on the moon must be no more than 1.0 km in diameter. staying within this diameter is accomplished by using a special large-diameter laser. part a if λ = 540nm , what is the minimum diameter of the circular opening from which the laser beam emerges? the earth-moon distance is 384,000 km. express your answer to two significant figures and include the appropriate units.

Mackinzie walks 4 blocks west, then 2 blocks south, then 4 blocks east, and, finally, 1 block south. what is the magnitude of her total displacement duringthis walk (in blocks)?

Aswimmer is determined to cross a river that flows due south with a strong current. initially, the swimmer is on the west bank desiring to reach a camp directly across the river on the opposite bank. in which direction shoud the swimmer head? a. the swimmer should swim southeast. b. the swimmer should swim south. c. the swimmer shuold swim northeast. d. the swimmer should swim due north. e. the swimmer should swim due east.