Question about calculating work?

Question

A 150 N boy rides a 60N bicycle a total of 200m at a constant speed. The fridtional force against the forward motion of the bicycle equal 35N. How much work does the boy do ?

I would think that its the 150N * 200M sicnce the question asked how much work does the boy do ?

Answer 1

Work is calculated by the product of force and the distance moved IN THE DIRECTION OF FORCE.

The boy’s weight is acting VERTICALLY DOWN.

The boy is not moving up or down.

No work is done by the force acting on the boy vertically down.

But the boy is moving horizontally 200 m.

The friction is acting opposite to the motion of the boy.

Against this friction the boy exerts a force in the direction of motion.

The force exerted by the boy is 35 N.

Since this force is exactly equal and opposite the net force on the boy is zero.

Hence he is moving with a constant speed.

The work done by the boy is 35 x 200 = 7000 joule.

But this work is not used to increase or decrease the speed of the boy.

We can calculate the work done by the friction also.

It is 35 x 200 = 7000 joule.

The work by friction always is converted into heat energy.

Thus the work done by the boy is converted into heat energy by way of the work done by friction.

If the work is not converted into heat the boy will move increasing speed.

Answer 2

Imagine that the bicycle is going forward and the force needed to keep it going forward is 35 N. The distance it is going forward is 200m. The formula for work is the W=Fd, assuming that the force and the distance are in the same direction.
W = (35N)(200m) = 7000 J.
The weight of the boy and bicycle are not relevant, since the force needed to keep them up is not in the same direction as the distance travelled.

Answer 3

shouldn't you be doing this on your own?

i would explain, but the guy above already did

Answer 4

i concur with the above