Question

If a 10 kg mass is dropped from a height of 20 meters, what will its velocity be just before hitting the
ground? (Ignore air resistance and assume g=9.8 m/s2).

Answer 1

To calculate the velocity of a 10 kg mass just before it hits the ground when dropped from a height of 20 meters, we can use the following kinematic equation:

\[
v^2 = u^2 + 2gh
\]

Where:
- \( v \) = final velocity (just before hitting the ground)
- \( u \) = initial velocity (which is 0 m/s since it is dropped)
- \( g \) = acceleration due to gravity (9.8 m/s²)
- \( h \) = height (20 m)

Substituting the values into the equation:

\[
v^2 = 0^2 + 2 \cdot 9.8 \, \text{m/s}^2 \cdot 20 \, \text{m}
\]

\[
v^2 = 0 + 2 \cdot 9.8 \cdot 20
\]

\[
v^2 = 392
\]

Now, take the square root to find \( v \):

\[
v = \sqrt{392} \approx 19.8 \, \text{m/s}
\]

Thus, the velocity of the mass just before hitting the ground will be approximately **19.8 m/s**.