Athin rod of length 1.3 m and mass 250 g is suspended freely from one end. it is pulled to one side and then allowed to swing like a pendulum, passing through its lowest position with angular speed 5.88 rad/s. neglecting friction and air resistance, find (a) the rod's kinetic energy at its lowest position and (b) how far above that position the center of mass rises. (a) number enter your answer for part (a) in accordance to the question statement units choose the answer for part (a) from the menu in accordance to the question statement

(a) 2.42 J

The kinetic energy of a rotating object is given by:

where

I is the moment of inertia

is the angular speed

Here we have

at the lowest point of the trajectory

While the moment of inertia of a rod rotating around one end is

And substituting in the previous formula, we find the kinetic energy at the lowest position:

(b) 0.99 m

According to the law of conservation of energy, the total mechanical energy (sum of kinetic energy and potential energy) must be conserved:

At the lowest point, we can take the potential energy as zero, so the mechanical energy is just kinetic energy:

At the highest point in the trajectory, the rod is stationary, so the kinetic energy will be zero, and the mechanical energy will simply be equal to the gravitational potential energy:

where h is the heigth of the centre of mass of the rod with respect to the lowest point of the trajectory. Solving for h, we find

gpe = mass x gravity constant x height or… gpe = mgh

where… mass: measured in kilograms (kg)

gravity: gravity constant on earth = 10.00 m/s2

height: measured in meters (m)

gpe: measured in joules (j) or kilojoules (kj)

how do you solve gpe?

gravitational potential energy (gpe) is the energy an object has because of its position above the. ground.

gpe = mass x gravity constant x height or… gpe = mgh.

mass:

note: to earn full marks when solving science word problems, you must show your work:

formula.

example:

given values:

mass = 0.3 kg.