Physics !!! Help ?

Question

A 73.3 kg bobsled is pushed along a horizontal surface by two athletes. After the bobsled is pushed a distance of 5.6 starting from rest its speed is 7.1 m/s. Find the magnituide of the net force on the bobsled. Answer in units of N.

Answer 1

You've missed a unit, but I'm going to assume the distance is 5.6 metres ...

(Velocity) = (Work) = (Force) * (Distance)

and

(Force) = (mass) * (acceleration)

therefore

(Force) = (mass) * (distance) / (velocity)

... plugging in the numbers, we get 57.8 kg.m/s/s ... = 57.8 N.

Answer 2

Net force on bobsled: Fnet = m.a (Eq. 1)

Since the mass m of the bobsled is known, you need to figure its acceleration a.

After time t, the bobsled, pushed from rest, travels the distance:
d = 0.5 * a * t^2 (Eq. 2)

The speed gained by being pushed from rest after the same amount of time t is:
v = a * t (Eq. 3)

Substitute Eq. 2 into Eq. 3:
d = 0.5 * a * t * t = 0.5 * v * t

You can find travel time: t = 2 * d / v

From Eq. 3:
v = a * t
<-> a = v / t
<-> a = v^2 / (2 * d)

From this you find a and substitute that value into Eq. 1 to find Fnet.