Question

A team of dogs drags a 121 kg sled 1.72 km
over a horizontal surface at a constant speed.
The coefficient of friction between the sled
and the snow is 0.205.
The acceleration of gravity is 9.8 m/s
2
.
Find the work done by the dogs.
Answer in units of kJ

Answer 1

A team of dogs drags a 121 kg sled 1.72 km over a horizontal surface at a constant speed. The coefficient of friction between the sled and the snow is 0.205. The acceleration of gravity is 9.8 m/s. Find the work done by the dogs. Answer in units of kJ.

$F_{fr}$ - friction force

$F$ - pulling force

Constant speed $\Rightarrow$ acceleration equals 0.

Newton's first law of motion:

$x: \quad F = F_{fr}$

$y: \quad N = mg$

Friction force equals $F_{fr} = \mu N = \mu mg, \mu$ - coefficient of friction.

Therefore:

$F = \mu mg$

The work done by a constant force of magnitude $F$ on a body that moves a displacement $d$ in the direction of the force is the product:

$W = Fd = \mu mgd = 0.205 * 121kg * 9.81\frac{m}{s^2} * 1720m = 419kJ$

Answer: $419kJ$