Question

A body of mass 10kg initially at rest is subjected to a force of 20N for 1second. Calculate the change in kinetic energy during that time.

Answer 1

Question #74276, Physics / Mechanics | Relativity

A body of mass $10\mathrm{kg}$ initially at rest is subjected to a force of 20N for 1 second. Calculate the change in kinetic energy during that time.

Need to find: K(kinetic energy)?

$$\mathbf{m} = 10 \mathrm{kg}$$ $$\mathbf{F} = 20 \mathrm{N}$$ $$\mathbf{t} = 1 \mathrm{s}$$

$\mathbf{u} = 0$, where $\mathbf{u}$ is initial velocity.

Solution:

According to first equation of motion, $v = u + a \cdot t$, where $\mathbf{a}$ – acceleration.

$$F = m \cdot a \rightarrow a = \frac{F}{m} = \frac{20 \mathrm{N}}{10 \mathrm{kg}} = 2 \frac{m}{s^2}$$

Then, $\pmb{v} = \pmb{0} + \pmb{2} \cdot \pmb{1} = \pmb{2} \frac{\pmb{m}}{\pmb{s}}$, $\pmb{K} = \frac{\pmb{m} \cdot \pmb{v}^2}{2} = \frac{\pmb{10} \cdot \pmb{2}^2}{2} = 20 \mathrm{~J}$

**Answer**: The change in kinetic energy during 1 second is equal $20\mathrm{~J}$

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