How much work is done by a person lifting a 5.0 kg object from the bottom of a w

Question

How much work is done by a person lifting a 5.0 kg object from the bottom of a will at a constant speed of 2.0 m/s for 5.0 s? A) 0.22 kJ B) 0.34 kJ C) 0.49 kJ D) 0.57 kJ A force F acts on a particle as the particle moves along the x axis. If the particle's initial kinetic energy is 20.0 J and after s minutes its kinetic energy is 522 J, at what rate this force doing work? A) 2.54 W B) 76.2 W C) 44.5 W D) 16.7 W The only force acting on an object as it moves along the positive x axis is F_x = 8 in meters. What is the net change in its Kinetic energy as it moves from x = -1 m? A) 60 J B) 49 J C) 19 J D) 17 J A tennis ball was released 3 m above the floor. It bounces back three time loses 25 % of its energy due to heating, how high does it rise after the third A) 120 mm B) 127 cm C) 140 cm D) 102 mm

Explanation / Answer

10. Work done W = force × distance.

Force = m× g = 5 kg × 9.81 m/s2= 49.05 N

Distance = speed× time = 2 m/s× 5s = 10 m

i.e. W = 49.05× 10 = 490.5 J = 0.49 KJ

(C) is the correct option

11.

Rate of doing work (P) = 522J-20J/5min. = 1.67 J/s = 1.67 W

(D) is correct option

12. Question is not completely visible

13.

Assuming total energy= 1 unit.

After first collision , energy = 1-0.25= 0.75

After second collision , E = 0.752

After third collision E = 0.753= 0.422 unit

0.422× mgh = mgh'

h'= 0.422× 3m = 1.265 m ~ 127 cm

(B) is correct option

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