Where does the 0.08 value come from in force calculation from momentum?

[coconut62]

Homework Statement

The question is in the first and second image. The question I am going to ask is c(ii).

I know one way of finding the force is to divide the momentum by the time, and my answer was correct.
But the marking scheme(third image) shows another way of doing it which includes an extra value of 0.08, and I don't know where does it come from. What exactly is it?

Homework Equations

1. F= p/t

2. F= mv/t

The Attempt at a Solution

Since the solution in the marking scheme used F= mv/t, and v/t = acceleration, so I tried calculating the acceleration. To no avail.

Positive velocity part: 9/2.4 = 3.75
3.75 x 0.78 = 2.9N, correct answer but no 0.08.

Negative velocity part: 6/1.6 = 3.75
Same as above.

I know this may seem a bit lame but I cannot feel comfortable if I don't find out where that 0.08 come from. Please help me, thanks.

 

[rude man]

The fault is the teacher's.

He/she miscomputed F = m delta v / delta t. The 0.08 looks like maybe a mistaken roundoff of 0.78 kg. But plainly and simply, that number does not belong there at all. The answer is 10.3/3.5 = 2.9N.

 

[coconut62]

Thank you.