Posted by **Matt** on Monday, March 12, 2007 at 4:53pm.

1st question: I was solving a question and I was asked the work done by friction. It is natural that work done by friction (a retarding force)should be negative and in my answer it was. However, just to be sure, work can be negative?

2nd question: A block of m = 2.00kg is moving a long a frictionless horizontal surface. The block reaches the relaxed spring (x ini. = 0) with an initial velocity of 6 m/s and compresses it to x final = 0.150m. At this value of compression, the speed of the block is reduced to v final = 4.00 m/s.

a) during this process, what is the change in Kinetic energy of the block?

sol) mv2(f)/2 - mv2 (i)/2 (correct?)

B) How much work has been done by the spring force on the block.

W(s)= mv2(i)/2 - mv2(f)/2

c) What is the spring constant of this spring. (hint: use work-kinetic energy theorem)

would it be x * whatever I get for part A?

Do any of the above answers make sense?

work done is negative when work is done on the system.

a correct

b correct

c No. change KE= 1/2 k x^2 solve for k.

## Answer this Question

## Related Questions

- physics - because of friction, a constant force of 20 N is needed to slide a box...
- ap Physics - 1. a)A 15.6 kg block is dragged over a rough, horizontal surface by...
- physics - A 280 kg piano slides 4.3 m down a 30° incline and is kept from ...
- Physics - A 2.32 kg block slide down a ramp from a height of 4.19 m. The block ...
- physics - Part 1 A 15.6 kg block is dragged over a rough, hor- izontal surface ...
- PHYSICS - I don't know where to start solving this question. Please help! A 320 ...
- Physics - Sally applies a horizontal force of 500 N with a rope to dtag a wooden...
- Physics (thx drwls, bobpursley) - After reaching terminal velocity, a raindrop ...
- Yet another science question.. - How much work is done when you push a 50kg ...
- mechanics_ physics - A trolley is use in pushing a book 1.20m along a horizontal...