Work and Power

A 2.50 × 105 W motor is used for 26.4 s to pull a boat straight toward shore. How far does the boat move toward shore if a force of 4.20 × 104 N is applied by the motor? 157 m 1,590 m 1.11 × 106 m 6.60 × 106 m

157 m

Natalia lifts a bag of groceries 0.50 m by exerting a force of 36 N. How much work did she do on the bag? 0 J 18 J 36 J 72 J

18 J

A 5,400 W motor is used to do work. If the motor is used for 640 s, about how much work could it do? 8.4 J 4,800 J 6,000 J 3,500,000 J

3,500,000 J

A crane does 9,500 J of work to lift a crate straight up using a force of 125 N. How high does the crane lift the crate? 0.013 m 76 m 9,400 m 1,200,000 m

76 m

In which scenario is an animal doing work? Check all that apply. A cat lifts up her kitten by its neck. A dog rubs his back against a large tree. A bird carries a worm to its nest. A goat butts its head against the barn wall. A horse pulls a wagon along a road.

A cat lifts up her kitten by its neck. A bird carries a worm to its nest. A horse pulls a wagon along a road.

In which scenario is the least amount of work done on a crate? A force of 120 N moves it 25 m. A force of 115 N moves it 26 m. A force of 130 N moves it 22 m. A force of 125 N moves it 27 m.

A force of 130 N moves it 22 m.

Trevor is pulling his younger brother in a wagon. He pulls the wagon 50 m to the corner with a force that is parallel with the ground. He then turns the wagon around and pulls it 50 m back to the starting point with the same force at an angle of 30° with respect to the ground. How does the amount of work Trevor performs going to the corner compare with the amount of work he performs coming back? They are the same because he uses the same amount of force. They are the same because he travels the same distance. He does less work coming back because the force moving the wagon is only 50cos30°. He does more work coming back because the force moving the wagon is only 50cos60°.

He does less work coming back because the force moving the wagon is only 50cos30°.

Brandi poses as Lady Justice for a skit in her government class. She holds a set of scales above her head with her right hand and a sword by her side in her left hand. She holds the pose for 10 minutes. At the end of the skit, she mentions to her friend that it was a lot of work to pose and that her arms were really tired. Which best summarizes Brandi's statement about doing work while posing? She did no work because she did not exert any forces on objects. She did more work using her right hand than her left because her right hand was higher. She did no work because she did not move the scales or sword while she posed. She did work the entire time she posed because she was tired at the end.

NOT She did work the entire time she posed because she was tired at the end. NOT She did more work using her right hand than her left because her right hand was higher.

Which statement about work and power correctly describes an automobile race? The cars do different amounts of work depending on how fast they finish. The car that finishes last has the lowest power. The car with the greatest power travels the greatest distance. The cars do different amounts of work depending on their power.

NOT The cars do different amounts of work depending on their power.

The rate at which work is done is

Power

A load of bricks is lifted to the second floor of a building. How do work and power relate to this job? The longer the job takes, the more work is done. The faster the job is done, the greater the power. The greater the power applied, the more work is done. The less work is done, the more power is needed.

The faster the job is done, the greater the power.

How do the units of work and power compare? The unit for work is a watt. The unit for power is a joule, which is a watt-second. The unit for work is a watt. The unit for power is a joule, which is a watt per second. The unit for work is a joule. The unit for power is a watt, which is a joule-second. The unit for work is a joule. The unit for power is a watt, which is a joule per second.

The unit for work is a joule. The unit for power is a watt, which is a joule per second.

Examine the scenarios. Scenario W: A force of 75 N moves a box 15 m. Scenario X: A force of 100 N moves a box 12 m. Scenario Y: A force of 50 N moves a box 20 m. Scenario Z: A force of 25 N moves a box 45 m. In which scenarios is the same amount of work done on the box? W and X W and Z X and Y Y and Z

W and Z

The use of force to move an object is

Work

Which best identifies the requirements for work to be performed? an object that has a force acting on it an object that is moving and has no net force a force acting on a motionless object a force that moves an object

a force that moves an object

Lester prepares to lift a heavy sack of flour into a customer's shopping cart. During which part of the action does Lester do work? when he applies force to the sack before lifting it when he holds the sack against his chest as he lets go of the sack and it falls onto a cart as he lifts the sack to his chest from the floor

as he lifts the sack to his chest from the floor

A force of 75 N at an angle of 15° to the direction of motion moves a chair 3 m. Which change would result in more work being done on the chair? using 60 N of force moving the chair 2 m increasing the angle to 20° decreasing the angle to 10°

decreasing the angle to 10°

How is power calculated? multiply force and displacement divide force by displacement multiply work and time divide work by time

divide work by time