T's peggy sue's birthday and she's about to blow out the candles on her cake. brother roger stops the party when he shouts: "look at that! chemical and physical changes taking places on your birthday cake! " how would you respond to roger? a) roger is incorrect. the melting wax is a physical change but there is no chemical change taking place. b) roger is correct. lighting the match is a chemical change and burning the candles is a physical change. c) roger is correct. the melting wax is a physical change and the burning candle wick is a chemical change. d) roger is incorrect. only a chemical change is taking place as evidenced by the light and heat of the burning candles.

D) Roger is incorrect. Only a chemical change is taking place as evidenced by the light and heat of the burning candles.

Explanation:

- A physical change is a change in which there is no formation of new substances. Examples of physical changes are the melting or the evaporation of a substance (all phase transitions are examples of physical changes): in such cases, there is no formation of new substances.

- A chemical change is a change in which new substances form. Examples of chemical changes are the chemical reactions: for instance, when a candle burns, a reaction is taken place (oxygen is burnt, transforming into carbon dioxide + heat + light, so this is an example of chemical change).

Therefore, the correct answer is

D) Roger is incorrect. Only a chemical change is taking place as evidenced by the light and heat of the burning candles.

the first american roller coaster was the mauch chunk switchback railway, built in the mountains of pennsylvania in the mid-1800s. the track, originally built to send coal to a railway, was reconfigured as a "scenic tour."

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.