# Newton's 2nd & 3rd law

(a) A snow sled with a child secured safely to it has a total mass of 56.0 kg. It is lowered at a constant speed of 1.1 m s−1 down a slope of angle 35.0 ° with respect to the horizontal (as shown above) for a distance d = 18.0 m. The coefficient of kinetic friction between the sled and the snow is 0.13.

Note: g = 9.8 m s–2. Air resistance is negligible at these speeds.

Find the magnitude of the reactive force, N, on the sled.

The correct answer should be 450.0 but my answer is different. I don't know how to solve this question but here's my attemp:

ΣFx = 1.1 cos 35.0° = 0.90
ΣFy = 1.1 sin 35.0 = 0.63

$$a = \frac{\sum F}{m}$$

ax = 0.90 ÷ 56.0 = 0.01
ay = 0.63 ÷ 56.0 = 0.01

Now to find the magnitude:

$$\sqrt{0.01^2 + 0.01^2} = 0.01$$ "?"

≠ 450.0 N

Thanks.

Last edited:

Nabeshin
The coefficient of kinetic friction between the sled and the snow is 0.13.

You failed to incorporate this into your solution. Taking this into consideration should help ^^

You failed to incorporate this into your solution. Taking this into consideration should help ^^

How can I incorporate that in my solution?

ƒk = μkn
$$ƒ = 0.13 \times n$$

So, what should I use for the n, the magnitude of the normal force?

Nabeshin