1)Sara, who weighs 66.0 kg, enjoys a 638-Calorie (638 kcal) breakfast of pancake

Question

1)Sara, who weighs 66.0 kg, enjoys a 638-Calorie (638 kcal) breakfast of pancakes loaded with fruits, cream, and syrup. She wishes to maintain her weight, so she decides to work out before going to her fitness group's weekly meeting. If the height of a single stair is 12.0 cm, and her body is only 25% efficient in converting chemical energy to mechanical energy, determine the number of stairs Sara must climb to cancel out the Calories consumed.

2)A piece of iron block moves across a rough horizontal surface before coming to rest. The mass of the block is 3.30 kg, and its initial speed is 2.30 m/s. How much does the block's temperature increase, if it absorbs 68% of its initial kinetic energy as internal energy? The specific heat of iron is 452 J/(kg · °C).

3)In a physics lab, students are conducting an experiment to learn about the heat capacity of different materials. The first group is instructed to add a number of 1.50 g pellets made of lead, at a temperature of 92.0°C, to 180 g of water at 16.0°C. A second group is given the same number of 1.50 g pellets as the first group, but these are now aluminum pellets. Assume that no heat is lost to or gained from the surroundings for either group.

(a) If the final equilibrium temperature of the lead pellets and water is 25.0°C, how many whole pellets did the first group use in the experiment? The specific heat of lead is0.0305 kcal/(kg · °C).
(b) Will the final equilibrium temperature for the second group be higher, lower, or the same as for the first group? The specific heat of aluminum is 0.215 kcal/(kg · °C).

(c) What is the equilibrium temperature of the aluminum and water mixture for the second group?

Explanation / Answer

There are multiple questions here. I am allowed to answer only 1 at a time. SO I will annwer question 1 for you. please post others as different questions.

1)
1 cal = 4.184 J
Energy consumed = 638 KCal
= 638000 * 4.184 J
= 2669392 J

Number of stairs cases she need to climb be n.
Total height = 12 cm * n = 0.12n metres
Increase in potential energy = m*g*h
= 66 * 9.8 * 0.12n
= 77.616 n

Energy converted = 25 % of 77.616n = 0.25 * 77.616n = 19.404n Joule

This energy should be equal to energy consumed.

19.404n = 2669392
n = 137569

Answer: 137569

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