Molecular Physics | Thermodynamics Answers

A 29.0 cm long spring is hung vertically from a ceiling and stretches to 35.7 cm when a 7.00 kg mass is hung from its free end.

(a)

Find the spring constant (in N/m).

 __N/m

(b)

Find the length of the spring (in cm) if the 7.00 kg weight is replaced with a 165 N weight.

__ cm

The system shown in the figure below is used to lift an object of mass m = 17.5 kg.

 A constant downward force of magnitude F is applied to the loose end of the rope such that the hanging object moves upward at constant speed. Neglecting the masses of the rope and pulleys, find the following.

(a) Find the required value of F.

 __N

(b) Find the tensions T₁, T₂, and T₃. (T₃ indicates the tension in the rope which attaches the pulley to the ceiling.)

T₁ =  __N

T₂ = __ N

T₃ = __ N

(c) Find the work done by the applied force in raising the object a distance of 1.70 m.

__ kJ

What average mechanical power (in W) must a 61.5 kg mountain climber generate to climb to the summit of a hill of height 345 m in 49.0 min? Note: Due to inefficiencies in converting chemical energy to mechanical energy, the amount calculated here is only a fraction of the power that must be produced by the climber's body.

__W

Under normal conditions the human heart converts about 13.3 J of chemical energy per second into 1.33 W of mechanical power as it pumps blood throughout the body.

(a)

Determine the number of Calories required to power the heart for one day, given that 1 Calorie equals 4186 J.

__ Cal

(b)

Metabolizing 1 kg of fat can release about 9000 Calories of energy. What mass of metabolized fat (in kg) would power the heart for one day?

__ kg

The force acting on a particle varies as in the figure below. (The x-axis is marked in increments of 5.00 m.)A coordinate plane has a horizontal axis labeled x (m) and a vertical axis labeled F_x (N). There are five points, connected by straight lines in order from A to E.

• Point A is at (0,0). Point B is at (20,6). Point C is at (40,0). Point D is at (50,−3). Point E is at (60,0).

Find the work done by the force as the particle moves across the following distances.

(a) from x = 0 m

 to x = 40.0 m

__ J

(b) from x = 40.0 m

 to x = 60.0 m

__ J

(c) from x = 0 m

 to x = 60.0 m

 __J

A student evaluates a weight loss program by calculating the number of times he would need to climb a 13.0 m high flight of steps in order to lose one pound (0.45 kg) of fat. Metabolizing 1.00 kg of fat can release 3.77 ✕ 10⁷ J of chemical energy and the body can convert about 22.0% of this into mechanical energy (the rest goes into internal energy.)

(a) How much mechanical energy (in J) can the body produce from 0.450 kg of fat?

__ J

(b) How many trips up the flight of steps are required for the 92.0 kg student to lose 0.450 kg of fat? Ignore the relatively small amount of energy required to return down the stairs.

 __trips

A hummingbird hovers by exerting a downward force on the air equal, on average, to its weight. By Newton's third law, the air exerts an upward force of the same magnitude on the bird's wings. Find the average mechanical power (in W) delivered by a 3.40 g hummingbird while hovering if its wings beat 55.0 times per second through a stroke 3.34 cm long.

__W

Find a) the mass in kilograms and b) rms speed for sulfur dioxide S02 at room temperature 20°C. mass5 = 32.065u

A ball is thrown 125 meters upward and then falls the same distance back on earth. Neglecting air resistance, its total time in the air is