A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is required?

How much work did the movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50?

A 1300-N crate rests on the floor. How much work is required to move it at constant speed 4.0 m vertically?

How much work must be done to stop a 1250-kg car traveling at 105 km/h?

Why is it tiring to push hard against a solid wall even though you are doing no work?

Why is it tiring to push hard against a solid wall even though you are doing no work on the wall?

Is the work done by kinetic friction forces always negative? $\it{[Hint}$: Consider what happens to the dishes when pulling a tablecloth from under your mom's best china.$]$

Is the work done by kinetic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under them.]

A $1200~\mathrm{N}$ crate rests on the floor. How much work is required to move it at constant speed $(a)$ $5.0 \mathrm{~m}$ along the floor against a friction force of $230 \mathrm{~N}$, and $(b)$ $5.0 \mathrm{~m}$ vertically?

Two tugboats pull a disabled supertanker. Each tug exerts a constant force of $1.90\times10^6~\text{N}$, one at an angle $19.0^\circ$ west of north, and the other at an angle $19.0^\circ$ east of north, as they pull the tanker a distance of $d=0.870~\text{km}$ toward the north. What is the total work done by the two tugboats on the supertanker? Express your answer in joules, to three significant figures.

For each of the cases described below, sketch and label the total acceleration vector, the radial acceleration vector, and the tangential acceleration vector. $(a)$ A car is accelerating from $55 \mathrm{~km} / \mathrm{h}$ to $70 \mathrm{~km} / \mathrm{h}$ as it rounds a curve of constant radius. $(b)$ A car is going a constant $65 \mathrm{~km} / \mathrm{h}$ as it rounds a curve of constant radius. $(c)$ A car slows down while rounding a curve of constant radius.

Suppose that the coefficient of kinetic friction between Zak's feet and the floor, while wearing socks, is $0.250$. Knowing this, Zak decides to get a running start and then slide across the floor. If Zak's speed is $3.00 \ \mathrm{\frac{m}{s}}$when he starts to slide, what distance $d$ will he slide before stopping?

Your dormitory has a nice balcony that looks over a pond in the grass below. You attach a 16-m-long rope to the limb of a tall tree beside the pond and pull it to the balcony so that it makes a $53^{\circ}$ angle from the vertical. You hold the rope while standing on the balcony and then swing down. (a) How fast are you moving at the lowest point in your swing? Specify the system and the initial and final states. List the assumptions that you made. (b) How strong should the rope be to withstand your adventure (use your own mass for calculations)?

(II) You are on a pirate ship and being forced to walk the plank (Fig. 12-67). You are standing at the point marked C. The plank is nailed onto the deck at point A, and rests on the support $0.75 \mathrm{~m}$ away from A. The center of mass of the uniform plank is located at point B. Your mass is $65 \mathrm{~kg}$ and the mass of the plank is $45 \mathrm{~kg}$. What is the minimum downward force the nails must exert on the plank to hold it in place?