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Keeping Soup Hot on a Delivery Robot

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Keeping Soup Hot on a Delivery Robot

Test five compartment designs and choose the one that meets the goal.

The robot test

Read about the team's tests and study the table. Then answer the questions.

Lunch on Wheels

The robotics team at Cedar Ridge Middle School built a small wheeled robot that carries lunch from the cafeteria to the library, where a study group eats. The trip, with its stops, takes about 30 minutes. In early trials the soup arrived only lukewarm. Team captain Imani Brooks set a goal: the soup must still be at least 60 °C when it arrives. There is also a limit. The robot's motors struggle with heavy loads, so the empty food compartment can have a mass of no more than 350 g.

The team built five compartments from the same size of plastic box and changed only the lining and the lid. Design A had no lining. Design B had a foam lining 2 cm thick. Design C had a lining of aluminum foil. Design D had the same foam lining as B with a layer of foil on the inside. Design E had the same foam lining as B, but its lid had a 2 cm gap where a sensor cable passed through.

Hot water stood in for soup, so no food was wasted during testing. For each test, the teacher poured 500 mL of water at 70 °C into a sealed jar and placed it in the compartment. The robot then drove the same 30-minute route along the same hallway, which stayed at about 22 °C. When the robot arrived, a student opened the lid and read the water temperature with a probe thermometer. The team tested each design three times. The table shows the average results.

Compartment Tests (start: 70 °C, average of 3 trials)
Design	Lining	Lid	Mass (g)	Temp after 30 min (°C)
A	None	Closed	200	44
B	Foam	Closed	320	61
C	Foil	Closed	230	48
D	Foam + foil	Closed	360	64
E	Foam	2 cm gap	320	50

1.

By how many degrees did the water in Design B cool during the trip? °C

2.

What was the independent variable in the team's tests?

A. The starting temperature of the waterB. The route the robot droveC. The lining and lid of the compartmentD. The water temperature after 30 minutes

3.

Circle each variable the team kept the same in every test.

4.

Which two designs should the team compare to find out how much the lid gap matters?

A. Designs D and EB. Designs B and EC. Designs A and ED. Designs B and D

5.

How many more degrees did the water cool in Design E than in Design B? °C

6.

Which design meets both the 60 °C goal and the 350 g mass limit?

A. Design DB. Design BC. Design AD. Design E

Explain and improve

Use the passage, the table and what you know about thermal energy.

7.

The water cooled in every design. Which statement describes the energy transfer during a trip?

A. Thermal energy moved from the hot water, through the box, into the cooler air.B. Cold moved from the hallway air, through the box, into the jar of water.C. Thermal energy moved from the cooler hallway air into the hot water.D. The water's thermal energy stayed in the jar, but its temperature dropped.

8.

Sort each possible change to the compartment by how it would likely affect the soup.

9.

The team also wants to deliver cups of yogurt that start at 4 °C through the same 22 °C hallway. How would the foam lining of Design B affect the yogurt?

A. It would slow the transfer of thermal energy from the air into the yogurt.B. It would have no effect, because foam affects hot food but not cold food.C. It would warm the yogurt faster, because foam keeps food warm.D. It would cool the yogurt below 4 °C by trapping cold inside the box.

10.

Design B only just meets the goal. Which next step is the best way to improve the design and test it fairly?

A. Test Design A again with water that starts hotter than 70 °C.B. Test Design E one more time with the lid gap facing the wall.C. Test Design D again on a shorter route so the water has less time to cool.D. Build a lighter version of Design D and test it 3 times on the same route.

11.

Which design should the team put on the robot right now? Write a claim, give evidence from the table and explain your reasoning about thermal energy transfer.