20 A block of mass 4.2 kg is projected with speed \( 14 \mathrm{~m} \mathrm{~s}^{-1} \) up an inclined plane making an angle \( 28^{\circ} \) with the horizontal. The dynamic coefficient of friction between the block and the inclined plane is 0.42 , and the static coefficient is 0.55 .
a After how much time will the block stop?
b What distance will the block cover?
c When the block stops, will it then slide down the plane, or will it stay at rest?
d In another experiment the same block is projected down the plane with the same speed as before. Will the block stop?