Question

(1) A 1,500 kg car is moving along a level road of 60 km/h. What work is required to stop the car?

(2) At room temperature, an oxygen molecule, with mass 5.31 x 10^(–26) kg, typically has a kinetic energy of 6.21 x 10^(–21) J. How fast is the molecule moving?

(3) A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the change in potential energy? (acceleration due to gravity g = 9.80 m/s2)

Answer 1

Question #84855, Physics / Mechanics | Relativity

(1) A 1,500 kg car is moving along a level road of 60 km/h. What work is required to stop the car?

Solution

$$W = K = \frac{1}{2}mv^2 = \frac{1}{2}mv^2$$ $$W = \frac{1}{2}(1500)\left(\frac{60}{3.6}\right)^2 = 208000\,J = 208\,kJ.$$

(2) At room temperature, an oxygen molecule, with mass $5.31 \times 10^(-26)$ kg, typically has a kinetic energy of $6.21 \times 10^(-21)$ J. How fast is the molecule moving?

Solution

$$v = \sqrt{\frac{2K}{m}} = \sqrt{\frac{2(6.21 \cdot 10^{-21})}{5.31 \cdot 10^{-26}}} = 484\,\frac{m}{s}$$

(3) A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the change in potential energy? (acceleration due to gravity $g = 9.80$ m/s²)

Solution

$$E = mgh = (7)(9.8)(1.2) = 82\,J.$$

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