Question

Jason takes off across level water on his jet-powered skis. The combined mass of Jason and his skis is 75 kg (the mass of the fuel is negligible). The skis produce a forward thrust of 200 N and have a coefficient of kinetic friction with water of 0.10. Unfortunately, the skis run out of fuel after only 90 s. What is Jason's top speed?

Answer options:

150 m/s

240 m/s

24 m/s

90 m/s

Answer 1

Given,

Mass of jason and his skis=m = 75kg

Thrust produced by skis (T) = 200N

Coefficient of kinetic friction(k)= 0.10

Time = 90 sec

Take, g= 10m/s^2

Since the friction force acts against the direction of thrust.

Therefore,

Net force (Fn)= m x a

Thrust - friction force = m x a

200 - 0.1 x 75 x 10 = 75 x a

125= 75 x a

a = 1.66m/s^2 (a is accelaration)

Now let us use the equation if motion

V = u + at   

here v= velocity at t=90 s

u = initial velocity

v = u + at

v = 0+ 1.66 x 90

V = 150m/s

Therefore

Maximum velocity was 150m/s

Thus option 1 is correct