A particle of mass 100 g is thrown vertically upwards with a speed of 5 m/s. The work done by the force of gravity during the time the particle goes up is     

Options

A. ` 0.5J`
B. ` -0.5 J`
C. ` -1.25 J`
D. `1.25 J`

Answer

C

Explanation

Kinetic energy at projection point is converted into potential energy of the particle during rise. Potential energy measures the work done against the force of gravity during rise.
`:. ` (- work done) = Kinetic energy = `1/2 mv^2`
or (-work done) `= 1/2 xx ((100)/(1000))(5)^(2) = (5 xx 5)/(2 xx 10) = 1.25 J`
`:.` Work done by force of gravity = `-1.25`.