Physics question...?

Question

Four of your friends are piled on a large inner tube, which is at rest on a frozen lake in the middle of winter. The mass of each of your friends is 65 kg, and the inner tube has a mass of 8.0 kg. You apply a horizontal force of 320 Newtons to them.

a. Assuming no friction, calculate their acceleration.

b. Assuming (mu) = 0.090, calculate their acceleration.

Answer 1

Assuming that you aren't moving by the tube rolling

F= ma

a=F/m

a= (320) / [(4)(65) + (8)]

a= 1.194029851 m/ s^2

Second part of the equation you use kinematics

F(total) = F - F(friction)= F - MF(normal) =320 - (.090)(4)(65)= 296.6

F= ma= 296.6

a = 296.6 / (4)(65) = 1.1407 m/s^2