Question

A 400- N kangaroo exerts a constant force on the ground during the first 0.60 m of a vertical jump. After the kangaroo's feet leave the ground it rises an additional 1.88 m. When the kangaroo caries a baby kangaroo in its pouch and jumps with the same force, it can rise only 1.78 m higher after its feet leave the ground. What is the weight of the baby kangaroo?

Answer 1

Consider the applied force as F.
Work done by the force, W = Fx h
Where h is the initial distance, h = 0.6 m
The work done by the force is used as potential energy of the kangaroo.
Fh = mg (h + H)
Where H = 1.88 m
F = mg (h + H)/h
= 400 x (0.6 + 1.88) / 0.6
= 1653.33 N

With the baby in its pouch, the weight of kangaroo is, W' = Mg
Here H' = 1.78 m
Fh = Mg (h + H')
Mg = Fh / (h + H')
= (1653.33 x 0.6) / (0.6 + 1.78)
= 416.81 N

Weight of the baby kangaroo = W' - W
= 416.81 - 400
= 16.81 N