How many rocks/min to mantain a constant speed

[tironci]

This is the problem i am trying to solve:

A child sits in a wagon with a pile of 0.60-kg rocks. If she can throw each rock with a speed of 10 m/s relative to the ground, causing the wagon to move, how many rocks must she throw per minute to maintain a constant average speed against a 2.0-N force of friction? I need to find change in m/ change in t for rocks/min

m/t = thrust/v , now i found thrust = (m/t)v -> (0.6kg/60s) 10m/s = 0.1 N

m/t = thrust/ v -> 0.1/10 = 0.01 kg/s if i turn this it kg/min 0.01/60 = 1.7x10^-4

but this doesn't seem to be the right correct answer?

Any help would be appreciated

 

[unscientific]

F = v(dm/dt)

2 = 10(dm/dt)
dm/dt = 0.2 (thats per second)

 

[thomate1]

.

I would approach this problem by first understanding the basic principles of motion and forces. The child throwing rocks is creating a force (thrust) that is counteracting the force of friction, allowing the wagon to maintain a constant speed. The equation for Newton's Second Law (F=ma) can be applied here, where F is the net force, m is the mass of the wagon and rocks, and a is the acceleration. In this case, we want to maintain a constant speed, so the acceleration is zero.

Next, we can look at the forces acting on the wagon. The child's throwing force (thrust) is the only force moving the wagon forward, while the force of friction is acting in the opposite direction. The equation for friction (Ff=μN) can be used here, where Ff is the force of friction, μ is the coefficient of friction, and N is the normal force (in this case, the weight of the wagon and rocks).

Now, we can set up an equation to solve for the number of rocks per minute needed to maintain a constant speed:

thrust - friction = 0

Substituting in the values given in the problem, we get:

(m/t)v - μN = 0

Solving for t, we get:

t = μN/(mv)

Plugging in the values, we get:

t = (0.2N)/(0.6kg x 10m/s) = 0.0333 s

To find the number of rocks per minute, we need to divide the time by 60 seconds:

Number of rocks per minute = 0.0333 s/60 s = 0.00055 rocks/min

Therefore, the child needs to throw approximately 0.00055 rocks per minute to maintain a constant average speed against a 2.0-N force of friction. This may seem like a small number, but it makes sense since the force of friction is relatively small compared to the force of thrust created by the child throwing rocks. I hope this helps!