Exercises about energy and work (2nd course ESO - Natural Sciences)

Some exercises to practice for the following exams:

1. A car of 350 Kg runs at a speed of 40 m/s. Which is its kinetic energy?

2. A ball of 3000 g falls at a speed of 100 km/h. Could you express its kinetic energy in kJ?

3. A chicken is on a roof. It leaves an egg of 80 g, that falls to the floor at a speed of 33 m/s. Which is its kinetic energy?

4. Your boss tells you: "I will pay you 3 $ for each J of work that you make today". You have to carry a wheelbarrow full of stones between two piles separated 30 m, applying a force of 100 N. If you make 1 travel each 5 minutes, how many $ will you earn per hour?

5. The kinetic energy of a lorry, when it moves at a speed of 40 km/h,  is of 2469.14 kJ. Which is the mass of the lorry? Express it in tones (Tm).

6. One troy ounce (oz t) is a mass magnitude used to gauge the mass of precious metals, that equals 31.1 grams. A brick of platinum, that falls at a speed of 40 km/h, has a kinetic energy of 15.43 J 
a) Which is the mass, measured in troy ounces, of this brick of platinum? 
b) It the density of platinum is 21450 kg/m3, which is the volume, in m3, occupied by this brick?
c) Express this volume in cm3

7. A bird, that weights 75 g, is situated at a height of 300 m. Which is its potential energy?

8. Your teacher has a mass of 90 kg. He walks upstairs. If the height of each step is of 12 cm, which will be the potential energy of your teacher after 39 steps? 

9. How many km/h are 10 m/s?

10. How many m/s are 540 km/h?

11. How many km/h are 45 m/s?

12. How many m/s are 126 km/h?

13. Knowing that 1 calorie (cal) is equal to 4.18 J, answer.

a) How many cal are 30 J?

b) How many kcal are 30 kJ?

c) How many J are 20.33 cal?

d) How many kJ are 123456789 cal?

14. A ball goes from A to B running only on the continuous black lines of this plot and choosing the shortest way of covering this travel. 

Answer the following questions.

a) Which is the distance travelled by the ball.

b) If the ball completes all the path in 30 s, which is its speed in m/s and in km/h?

c) If the mass of the ball is of 750 g, which is its average kinetic energy?

d) Imagine that the ball increases its mass and, maintaining its speed, its average kinetic energy is now of 41.24 cal. How many grams has gained the ball?

15. In a strange planet called Villarrumbrar, only visible in the way between two small spanish villages, the potential energy of a person of 100 kg situated on the top of a building of 100 m of height, is 23 kJ. 

a) Which is the value of the gravity in this planet?

b) How is the mass of this planet compared to Earth's mass? 

Answers: 
1. 280000 J
2. 1.16 kJ
3.  4356 J
4. 108000 $/hour
5. 40 Tm
6. a) 8.04 oz t ; b) 0.000012 m3 ; c) 12 cm3 
7. 225 J
8. 4212 J
9. 36 km/h
10. 150 m/s
11. 162 km/h
12. 35 m/s
13. a) 7.18 cal ; b) 7.18 kcal ; c) 85 J ; 516049.38 kJ
14. a) 25.12 m ; b) 19.05 m/s and 68.58 km/h ; c) 136.08 J and 32.55 cal ; d) 200 g

15. a) 23 m/s2 ; b) the mass is higher in the planet than in Earth