Physics -- check answers

1. In moving an object of mass 10 kg through a distance of 8.0 m, 40 J of work is done. The average force exerted is?

my answer: 320N

2. What is the kinetic energy of a 20 kg object moving at a speed of 10 m/s?

my answer: 1000J

3. the gravitational potential energy of a bird of mass 2.0 kg on a tree branch of height 15 m is most nearly

my answer: 300J

4. Two objects have the same mass. One is travelling twice as fast as the other. The work that must be done to stop the faster object compared to the work required to stop the slower object is:

a)two times greater
b)the same
c)four times greater
d)half as great
e)one quarter as great

my answer: a

5. When a rock is thrown straight up in the air, after it leaves the hand, the rock begins to slow down. This occurs because:

a) the rock is gaining potential energy as it rises and thus it must lose kinetic energy
b)the force of gravity acting on the rock increases as the rock rises
c)the forces acting on the rock are balanced
d)the potential energy of the rock decreases as the rock rises

my answer: d

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  1. I believe that for 1 the answer is 5N. Work = Force * Distance and since we have two of those variables we can figure out the other one. We can substitute 40 J for W and 8 m for D.
    40J = F * 8m
    Then we isolate F so we can solve for it.
    40J/8m = F
    5N = F

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