9. Work & Energy

Intro to Calculating Work

Multiple Choice
You pull a 5kg box vertically up with a constant 100N force for 2m. How much work do you do?
Multiple Choice
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.
Multiple Choice
A $1000 kg$ pallet of bricks is being lowered to the ground by a crane. If the bricks are moving at a constant speed, how much work is done by the cable on the bricks as they descend $11 m$ ?
Multiple Choice
A particle of mass $250 g$ moving along the x axis has velocity $v_{x} = (7.6 x^{3}) m / s$ with x measured in m. How much work is done on the particle as it moves from $x = 0.0 m$ to $x = 2.0 m$ ?
Open Question
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. (e) What is the total work done on the crate?
Open Question
Two tugboats pull a disabled supertanker. Each tug exerts a constant force of 1.80×106N, 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?
Open Question
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. (d) How much work is done on the crate by the normal force? By gravity?
Open Question
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.(b) How much work is done on the crate by this force?
Open Question
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. (a) What magnitude of force must the worker apply?
Open Question
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. (c) How much work is done on the crate by friction?
Open Question
(I) A 55.0-kg firefighter climbs a flight of stairs 28.0 m high at constant speed. How much work does she do?
Open Question
(II) 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.
Open Question
A 25 kg air compressor is dragged up a rough incline from r₁ (→ above r)= (1.3î + 1.3ĵ) m to r₂ (→ above r) = (8.3î + 2.9ĵ) m, to where the y-axis is vertical. How much work does gravity do on the compressor during this displacement?
Open Question
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 p. Assume that the fluid is nonviscous so that friction with the pipe walls can be neglected. (a) 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?
Open Question
A 1000 kg elevator accelerates upward at 1.0 m/s² for 10 m, starting from rest. (b) How much work does the tension in the elevator cable do on the elevator?