Dancers experience large forces associated with the jumps they make. For example, when a dancer lands after a vertical jump, the force exerted on the head by the neck must exceed the head's weight by enough to cause the head to slow down and come to rest. The head is about 9.4% of a typical person's mass. Video analysis of a 65-kg dancer landing after a vertical jump shows that her head decelerates from 4.0 m/s to rest in a time of 0.20 s. Compared with the force her neck exerts on her head during the landing, the force her head exerts on her neck is: a. the same
b. greater
c. smaller
d. greater during the first half of the landing and smaller during the second half of the landing.

Explanation:

The head decelerates from 4 m /s to zero in .2 sec so deceleration = 4 - 0 / .2

= 20 m/s²

If F be the average force acting on head

F - mg = ma

F = m ( g + a )

= 65 ( 9.8 + 20 )

= 1937 N .

This force will be uniformly acting on head in upward direction . So during first half and second half , deceleration is same hence force F will also be same .

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f=ma newton

f=100x2.5=250n