Freefall

An object falls from the top of a building that is 25 m high. Air resistance is negligible. What is the speed of the object when it hits the ground?

• 10 ms^-1

• 22 ms^-1

• 25 ms^-1

• 65 ms^-1

Answer explanation

$v_0=0\ ms^{-1}\left(from\ rest\right)$
$h=-25\ m$
$g=-10\ ms^{-2}$
$v=?$
$v^2=v_0^2\ +2gh$
$v^2\ =0+2\times\left(-10\right)\times\left(-25\right)$
$v^2=500$
$v\ =22.36\ ms^{-1}$

Free fall is the condition when the only force acting on the object is the force due to gravity.

• True

• False

Answer explanation

The bodies are dropped from a height near the earth’s surface due to gravitational force. The fall of the bodies is called free fall.

A table-tennis ball is released from the top of an evacuated tube which means there is no air in the tube. Which graph shows how the speed of the ball changes with time as it falls to the bottom of the tube?

• A

• B

• C

• D

Answer explanation

The more the time is, the more speed of the tennis ball falls to the bottom.

Therefore graph A shows the speed and time relation.

Gravitation field strength is numerically equal to the acceleration due to gravity.

• True

• False

At what rate do objects accelerate toward Earth in freefall condition?

• It depends on the mass of the object

• It depends on the size of the object

• At 9.8 ms^-2 near the surface of the Earth

• At 9.8 ms^-2, no matter how far you are above the Earth

Answer explanation

When the bodies are dropped from a height near the earth’s surface, they will fall onto the ground with constant acceleration. This acceleration due to gravitational force is

9.8 ms^-2.

Which force do we ignore during free fall motion problems?

• Gravitational force

• Magnetic Force

• Tension force

• Air resistance

Answer explanation

Air resistance is negligible in free fall condition.