Question

A body of mass 0.5kg is thrown vertically upwards from the ground with an initial velocity of 80.0m/s

Answer 1

Answer:

1)        3.92 J

2) 1596.08 J

3)         16.3 s ??

Explanation:

Initial Potential energy PE = mgh = 0.5(9.8)(0) = 0 J

Initial Kinetic energy KE = ½mv² = ½(0.5)80² = 1600 J

PE = 0.5(9.8)(0.80) = 3.92 J

KE = 1600 - 3.92 = 1596.08 J

Question 3 is not clear

to the point 80 cm above the ground the flight time is only 0.01 s

The time when the mass strikes ground again will be twice the time gravity takes to reduce the initial velocity to zero

t = 2(80.0 / 9.8) = 16.3 s

would not 80 m above the ground be a much more interesting point to consider?

PE = 0.5(9.8)(80) = 392 J

KE = 1600 - 392 = 1208 J

v₈₀ = √(2(1280) /0.5) = 69.5 m/s

t₈₀  = h/v(avg) = 80 / (½(80 + 69.5)) = 1.07 s