Q. A bullet of mass 10 g is fired horizontally with a velocity 1000 ms-1 from a rifle situated at a height 50 m above the ground. If the bullet reaches the ground with a velocity 500 ms-1, the work done against air resistance in the trajectory of the bullet is (take g = 10 m-2)
1) 5005 J
2) 3755 J
3) 3750 J
4) 17.5 J
Answer:
2) 3755 J
Solution:
Work done against the air resistance is the energy lost
W = (mgh + (1/2)mu2)- (1/2)mv2
= (1/2)m(u2 – v2) + mgh
= (1/2) 10-2(10002 – 5002) + 10-2 x 10 x 50
= (1/2)10-2 x 750000 + 10-2 x 500
= (1/2)7500 + 5
= 3750 + 5
= 3755 J