A large rock is motionless on a flat sidewalk. Which statement best explains why the rock remains motionless? There are no forces acting on the rock.

The sidewalk exerts an unbalanced force on the rock.

The only force acting on the rock is directed at the sidewalk.

The forces acting on the rock are all balanced.

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Which of the following is an indication that a substance has undergone a chemical change? a. no new product has been formed. b. the color of the substance has not changed. c. the original constitute has not changed. d. the molecular structure has changed.

Listenbase your answer to the question on the information below. nuclear radiation is harmful to living cells, particularly to fast-growing cells, such as cancer cells and blood cells. an external beam of the radiation emitted from a radioisotope can be directed on a small area of a person to destroy cancer cells within the body. cobalt-60 is an artificially produced radioisotope that emits gamma rays and beta particles. one hospital keeps a 100.0-gram sample of cobalt-60 in an appropriate, secure storage container for future cancer treatment. which choice represents the correct product for the beta decay of the co-60? fe-60ni-60fe-61ni-61