Question

24) How much work is performed by friction in slowing a 10kg object from 4 m/s to 2 m/s? 25) To avoid an accident, you slam on your brakes, skidding for a distance of 40 m before you stop. (Your anti-lock brakes were malfunctioning!). Assuming a coefficient of kinetic friction of 0.8 between your tires and the road, how fast were you going before slamming on the brakes? 26) A 1-kg block is held below a vertically mounted spring - attached to the spring, but not yet pulling down on it. The block is released and falls, stretching the spring. The spring stretches 4 cm when the block is at its lowest position. What is the spring constant of the spring?

Answer 1

ey given m=10kg, V = 2m/s , Vi= umls - all the change in Kinetic Work done forees energy (In this case - only Work fiction is appear so onty done only by friction that We - (KE) - (KE); Wf = 1 mv - I m vi WF = X10 X(2)2 - 4 x 10X4) We = 20- 80 - We = -60J -ve sign act opposite only represent direction of that friction displace ment force

(25 to first sind out the acceleration due friction - Finet = ma - Mxing = ha r-resign becouse friction act opposite dion of motion given a=-ukg 4x=0.8, g = 9.81 m/s2 a= - 0.8X9.8 m/s2 a=-7.848 m/s² distance object is stoped after the of 1 s=yom vo v2 = 4² tas TO= 447 2x (-7-848) x40 0 = ² - 627.84 4²= 627.84 re= 25.056 m/s

6 m= 1 kg x=4cm Be = 4x10-2m feletee tritia In this case - energy is Conserved. and potential energy of Block is converted into potential energy of spring. - final (PE) block - (PE) spring mgx = 1 kxt mg = kx 199.81 = KCUX102) I 2 2 X 102 (K = 490.5 /m Ans