A man sits with his back against the back of a chair, and he pushes a block of m

Question

A man sits with his back against the back of a chair, and he pushes a block of mass m = 3 kg straight forward on a table in front of him, with a constant force F = 31 N, moving the block a distance d = 0.6 m. The block starts from rest and slides on a low-friction surface. (Due to the nature of this problem, do not use rounded intermediate values in your calculations—including answers submitted in WebAssign.)

CORRECT(a) How much work does the man do on the block? 18.6 Correct: Your answer is correct. J

CORRECT(b) What is the final kinetic energy K of the block? 18.5856 Correct: Your answer is correct. J

CORRECT(c) What is the final speed v of the block? 3.52 Correct: Your answer is correct. m/s

CORRECT(d) How much time t does this process take? .3406 Correct: Your answer is correct. s

CORRECT(e) Consider the system of the man plus the block: how much work does the chair do on the man?

CORRECT (f) What is the internal energy change of the man? -18.6 Correct: Your answer is correct.

Now suppose that the man is sitting on a train that is moving in a straight line with speed V = 19 m/s, and you are standing on the ground as the train goes by, moving to your right. From your perspective (that is, in your reference frame), answer the following questions.

CORRECT(g) What is the initial speed vi of the block? 19 m/s

CORRECT(h) What is the final speed vf of the block? 22.52 m/s

CORRECT(i) What is the initial kinetic energy Ki of the block? 541.5

CORRECT(j) What is the final kinetic energy Kf of the block? 760.7256

CORRECT(k) What is the change in kinetic energy K = Kf Ki? 219.2256

NEED HELP(l) How far does the block move (x)?

NEED HELP(m) How much work does the man do on the block?

NEED HELP(n) How far does the chair move?

NEED HELP(o) Consider the system of the man plus the block: how much work does the chair do on the man?

NEED HELP(p) What is the internal energy change of the man?

Explanation / Answer

l.) Acceleration of the block = force / mass = a = 31 / 3 = 10.33333 m/ s2

Initial velocity u = 19 m/s

final velocity v = 22.52 m/s

v2 - u2 = 2as

=> 22.522 - 192 = 2x 10.333333 x s

s = 7.0718 m

m.) by law of conservation of energy the change in kinetic energy of block as been given by the man

so work done by man on the block is = K = Kf Ki = 219.2256 J

n.) The chair moves along with the train whose speed is given as 19m/s

so, distance moved by chair = speed x time = 19 x 0.3406 = 6.472 m

o.) since the man is pushing the block with a force 31N , he is applying a force of 31 N on the chair with his back and in return the chair is applying an equal force of 31N on him.

So work done by chair on the man is = force x distance travelled by man

= 31 x 6.472 = 200.64 J

p.) Now, in this case, the change in KE of the block (219.2256 J) is given by the work done by the chair and also by the man.

So work transferred by man + work by chair = 219.2256

work by man + 200.64 = 219.2256

work by man = 18.5856 J

So, the change of internal energy in him will be the negative of the work done by him = > - 18.5856 J

After all, by intuition you can feel that you need to spend the same amount of energy to carry a bag inside or outside the train for the same distance.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.