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ENERGY & MOVEMENT COURSE

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Physics 3rd Partial Review
I. WORK & ENERGY SECTION
1. How much work will make (horizontally) the workers that move a 150 kg box a distance of 12.3 m through a rough floor if the friction’s coefficient is 0.70
Answer: 12,657 J

2. What is the minimum work needed to push a 1000 kg car 300 m up a hill with a 17.5° slope if there isno friction.
Answer: 8.8x105 J

3. What is the minimum work needed to push a 1000 kg car 300 m up a hill with a 17.5° slope if there is a friction’s coefficient of 0.25.
Answer: 1.6x106 J

4. What is the maximum speed at which a 40 kW engine can lift a 800 kg mass?
Answer: 5.10 m/s

5. A person takes down, using a rope, a 40 kg box from the roof of a 4.5 m high house in 3.5 s. Calculatethe power generated.
Answer: 1,764 watt

6. Calculate the power of a machine that lifts a 20 tons mass a high of 15 m in 2 minutes.
Answer: 588,000 watt

7. A 30 g bullet is fired at 1500 km/h. If the bullet penetrates a wood block, what is the work that the block of wood makes on the bullet to stop it?
Answer: 2,604 J

8. A constant net force of 75 N acts on an object initially at restthrough a parallel distance of 0.60 m.
(a) What is the final kinetic energy of the object?
(b) If the object has a mass of 0.20 Kg, what is its final speed?
Answer: (a) 45 J, (b) 21 m/s.

9. If the work required to speed a car up from 10 km/h to 20 km/h is 5x103 J what would be the work required to increase the car’s speed from 20 km/h to 30 km/h?
Answer: 8.3 x103 J.

10. What is thegravitational potential energy, relative to the ground, of a 1 kg box at the top of a 50 m building?
Answer: 490 J.

11. A 0.20 kg stone is thrown vertically upward with an initial velocity of 7.5 m/s from a starting point 1.2 m above the ground.
(a) What is the potential energy of the stone at its maximum height relative to the ground?
(b) What is the change in the potential energy of the stonebetween its launch point and its maximum height?
Answer: (a) 8 J, (b) 5.6 J.

12. A 0.300 kg ball is thrown vertically upward with an initial speed of 10 m/s. If the initial potential energy is taken as zero, find the ball’s kinetic, potential, and mechanical energies…
(a) at its initial position, Answer: (a) 15 J, zero, 15 J; (b) 7.65 J, 7.35 J, 15 J; (c) zero, 15 J, 15 J.
(b) at 2.50 m abovethe initial position, and
(c) at its maximum height.

13. A 0.50 kg ball thrown vertically upward with an initial kinetic energy of 80 J. (a) what are its kinetic and potential energies when it has traveled three fourths of the distance to its maximum height?
(b) What is the ball’s speed at this point? (c) What is its potential energy at the maximum height? (Assume a reference is chosen to bezero at the launch point.) Answer: (a) 20 J, 60 J; (b) 8.9 m/s, (c) 80 J.

Thermal Energy
Temperature
1. For each of the following temperatures, find the equivalent temperature on the indicated temperature scale: (a) –273.15°C on the Fahrenheit scale, (b) 98.6°F on the Celsius scale, and (c) 100 K on the Fahrenheit scale. Answers -4600C, 37.00C, 2800F

2. Which of the following is the hottesttemperature: 10 °C, 10 °F, 10 K or -10 K.

3. If the temperature drops by 10 °C, what is the corresponding temperature change on the Fahrenheit scale? Answer: 18 °F

4. Convert the following temperatures to their values on the Fahrenheit and Kelvin scales. (a) the boiling point of liquid hydrogen –252.87°C; (b) the temperature of a room at 20°C. Answers -4230F, 20.28 K and 680F, 293 K

5.Show that the temperature –40° is unique in that it has the same numerical value on the Celsius and Fahrenheit scales.

Thermal Expansion
6. A copper telephone wire has essentially no sag between poles 35.0 m apart on a winter day when the temperature is –20.0°C. How much longer is the wire on a summer day when TC = 35.0°C? Assume that the thermal coefficient of copper is constant throughout...