Question

a block of mass 4.5kg is free to move along the x axis. it is at rest at t= 0 . if the force on the particle varies with time then its kinetic energy at t =4.5 is​

Answer 1

first find change in momentum.

change in momentum = Area under F- t graph

[ from Newton's 2nd law, you know rate of change of momentum per unit time is known as force. i.e., F = dP/dt

so, P = ∫F.dt means, momentum is area under F - t graph. ]

now, momentum = 1/2 × 4N × 3s - 1/2 × 2N × (4.5s - 3s)

= 6kgm/s - 1.5 Kgm/s

= 4.5 Kgm/s

now, kinetic energy , K = P²/2m

where P is momentum and m is mass of particle.

so, kinetic energy at (t = 4.5s) = (4.5)²/2(4.5)

= (4.5 × 4.5)/9

= 4.5/2

= 2.25 J

hence, option (1) is correct choice.

Answer 2

Answer:

2.25 J is the answer................