Review Conceptual Example 16 as background for this problem. The water skier there has a mass of 73 kg. Find the magnitude of the net force acting on the skier when (a) she is accelerated from rest to a speed of 11 m/s in 8.0 s and (b) she lets go of the tow rope and glides to a halt in 21 s.

a) F = 100.375 N

b) F = 38.252 N

Explanation:

a) she is accelerated from rest to a speed of 11 m/s in 8.0 s

We get the acceleration we use this equation,

v = u + at

where v is the final velocity - 11 m/s

u = initial velocity = 0 m/s (from rest)

t is time taken = 8 s

Since v = u + at  

11 = 0 + a×8

8a = 11

a = 11/8 = 1.375

a = 1.375 m/s²

The force equation is given by:

F = ma

F is the force, m is mass = 73 kg and a is acceleration

F = 73 × 1.375 = 100.375

F = 100.375 N

(b) she lets go of the tow rope and glides to a halt in 21 s.

We get the acceleration we use this equation,

v = u + at

where v is the final velocity = 0 m/s (to a halt)

u = initial velocity = 11 m/s

t is time taken = 21 s

Since v = u + at  

0 = 11 + a×21

21a = -11

a = -11/21 = -0.524

a = 0.524 m/s²

The force equation is given by:

F = ma

F is the force, m is mass = 73 kg and a is acceleration

F = 73 × 0.524 = 38.252

F = 38.252 N

none, its a machine