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(v^{2} -u^{2})

=1/2*70*(2.5^{2}-5^{2})

=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.

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