If a block of mass 2 kg is pulled up on a smooth incline of angle 300 with horizontal and the block moves with an acceleration of 1 ms/2, then a) Find the power delivered by the pulling force at a time 4 seconds after motion starts. b) What is the average power delivered during these four seconds after the motion starts?
Resolving the forces parallel to incline F – mg sin ϴ = ma F = mg sin ϴ + ma = 2 x 9.8 x sin 300 + 2 x 1= 11.8 N The velocity after 4 seconds = u + at = 0 + 1 x 4= 4 m/s Power delivered by force at t =4 seconds = force x velocity = 11.8 N x 4 s = 47.2 W The displacement during 4 seconds is given by v 2 = u2 + 2 a s = 0 + 2 x 1 x s s =8 m The work done in 4 seconds = force x distance 11.8 x 8 = 94.4 J Average power delivered = work done / time = 94.4 / 4 = 23.6 V
