Question

a brick of mass 5 kg is released from rest at a height of 3 m. how fast is it going when it hits the ground? acceleration due to gravity is ( g = 9.8 m/s^2 ).

a. 8.1 m/s
b. 7.7 m/s
c. 7.2 m/s
d. 9.9 m/s

Explanation:

Step1: Apply the kinematic equation

The kinematic equation \(v^{2}=u^{2}+2as\) is used. Here, the initial velocity \(u = 0\ \text{m/s}\) (released from rest), acceleration \(a = g=9.8\ \text{m/s}^{2}\), and displacement \(s = 3\ \text{m}\).

Step2: Substitute the values into the equation

Substitute \(u = 0\), \(a = 9.8\), and \(s = 3\) into \(v^{2}=u^{2}+2as\). We get \(v^{2}=0^{2}+2\times9.8\times3\).

$$v^{2}=58.8$$

Step3: Solve for \(v\)

Take the square - root of both sides: \(v=\sqrt{58.8}\approx8.1\ \text{m/s}\)

Answer:

A. \(8.1\ \text{m/s}\)