1. A block of 20 kg is pulled up by applying a force acting parallel to the slope. If the slope makes an angle of 30 degree with the horizontal, calculate the work done in pulling the load by a distance of 3m. What is the increase in potential energy of the block. (g = 10 newton per kg)
2. The speed of a bicycle decreases from 18 to 9 kmph. If the total mass of cyclist including the cycle is 70 kg, calculate the work done in overcoming the friction offered by the brakes & the road. Does the kinetic energy of the system also reduce to half its initial value?
1.mass = 20kg
weight=force=20*10=200N
s=3m
w.d=fs
=200*3
=600J
potential energy=600J
2.u=18kmph=5m/s
v=9kmph=2.5m/s
w.d=change in K.E=1/2m(v2 -u2)
=1/2*70*(2.52-52)
=35*7.5*-2.5
=-656.25J
change in k.e=656.25J(as w.d is a scalar quantity)
initial k.E=1/2*70*5*5
=875J
final K.E=initial K.E-change in K.E
=875-656.25
=218.75J
no k.E o not reduce by half.It reduced by one fourth.