Question

If you apply 1.0 N of force to lift an object with a single-fixed pulley, then what is the resistive force?

A man pulls a box with a rope parallel to the ground. He pulls the box 100.0 m and does 5,000 J of work. What was the mass of that box?

A man begins pushing a lawn mower across a lawn from a standing start. Which statement is true?
A. Man is decreasing kinetic energy (KE) of lawn mower.
B. KE of lawn mower is not changing.
C. Man is increasing KE of lawn mower.
D. Cannot tell

Answer 1

1) Make a free body diagram and suppose acceleration = 0.

You will find that the force applied (1.0 N) equals the resistive force (the weight of the object). Then the resistive force = 1.0 N

2) Work = force * parallel distance ==> force = Work / parallel distance

Force = 5000 J / 100.0 m = 50 N

Force = mass * acceleration

Then to find the mass you need the acceleration. Given that there is not data to find the acceleration this part has not solution.

3) The answer is C. Man is increasing KE of lawn mower.

Explanation: KE = Kinetic energy, is proportional to velocity.

Given that initially the lawn mower is standing, its initial KE is zero. When it is moving the KE is greater than zero.