9. Work & Energy

You pull a 5kg box vertically up with a constant 100N force for 2m. How much work do you do?

You push a 3kg box against a wall for a distance of 2m with a force of 40N that makes a 53° angle with the horizontal, as shown. Calculate the work done by gravity.

A factory worker pushes a $30.0$-kg crate a distance of $4.5$ m along a level floor at constant velocity by pushing horizontally on it. The coefficient of kinetic friction between the crate and the floor is $0.25$. What is the total work done on the crate?

Two tugboats pull a disabled supertanker. Each tug exerts a constant force of $1.80\times {10}^6$ N, one $14°$ west of north and the other $14°$ east of north, as they pull the tanker $0.75$ km toward the north. What is the total work they do on the supertanker?

A factory worker pushes a $30.0$-kg crate a distance of $4.5$ m along a level floor at constant velocity by pushing horizontally on it. The coefficient of kinetic friction between the crate and the floor is $0.25$. How much work is done on the crate by the normal force? By gravity?

A factory worker pushes a $30.0$-kg crate a distance of $4.5$ m along a level floor at constant velocity by pushing horizontally on it. The coefficient of kinetic friction between the crate and the floor is $0.25$. How much work is done on the crate by this force?

A factory worker pushes a $30.0$-kg crate a distance of $4.5$ m along a level floor at constant velocity by pushing horizontally on it. The coefficient of kinetic friction between the crate and the floor is $0.25$. What magnitude of force must the worker apply?

A factory worker pushes a $30.0$-kg crate a distance of $4.5$ m along a level floor at constant velocity by pushing horizontally on it. The coefficient of kinetic friction between the crate and the floor is $0.25$. How much work is done on the crate by friction?

A 55.0-kg firefighter climbs a flight of stairs 28.0 m high at constant speed. How much work does she do?

Estimate the work you do to mow a lawn 10 m by 20 m with a 50-cm-wide mower. Assume you push with a horizontal force of about 15 N.

A 25 kg air compressor is dragged up a rough incline from ${\vec{r}}_1=(1.3\hat{ı}+1.3\hat{ȷ})\text{m}$ to ${\vec{r}}_2=(8.3\hat{ı}+2.9\hat{ȷ})\text{m}$, to where the y-axis is vertical. How much work does gravity do on the compressor during this displacement?

The energy used to pump liquids and gases through pipes is a significant fraction of the total energy consumption in the United States. Consider a small volume V of a liquid that has density ρ. Assume that the fluid is nonviscous so that friction with the pipe walls can be neglected. An upward-pushing force from a pump lifts this volume of fluid a height h at constant speed. How much work does the pump do?

A 1000 kg elevator accelerates upward at 1.0 m/s² for 10 m, starting from rest. How much work does the tension in the elevator cable do on the elevator?