A2.80 kg ball is attached to a ceiling by a 1.40 m long string. the height of the room is 3 m. what is the gravitational potential energy of the ball relative to (a) the ceiling? (b) the floor? (c) a point at the same elevation as the ball?

Answer

(a) -38.416 Joules.

(b)  43.904 Joules

(c) 0.00 Joules

Explanation

Gravitational potential energy (P.E) is the energy possessed by a body that is at a potential height from the ground.

IT is calculated by the formula;

P.E = mgh

Where m ⇒ mass

            g ⇒ acceleration due to gravity

            h ⇒ height from the ground.

(a) m = 2.8 kg, h = 1.40 m and  g = 9.8 m/s²

Relative to ceiling, the ball is lower, hence the grativational potential energy is lower (negative)

P.E = 2.80 × -1.40 × 9.8

      = -38.416 Joules.

(b) m = 2.80 Kg, h = 3-1.4=1.6 m and g = 9.8 m/s²

P.E = 2.80 × 1.6 × 9.8

        = 43.904 Joules

(c) m= 2.80 Kg, h = 0 m and g = 9.8 m/s²

P.E = 2.80 × 0 × 9.8

       = 0 Joules

There is no relative distance between the two points. So, the energy is zero.

total distance travelled = 60 miles

total time taken =1.5 hours

average speed = total distance / total time

60 / 1.5

= 40

therefore, average speed = 40 m/h

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