A student foolishly attempts to stop a steel bar, of length L = 1 m and at a temperature of 20ºC, from thermally expanding by attaching it to a wooden support with a nail at each end. Steel's Young's modulus is Y = 2.9 × 1011 N/m2 and it's linear thermal expansion coefficient is α = 12.1 × 10-6 1/C.

Y = 2.9 × 1011 N/m2
α = 12.1 × 10-6 1/C

a) Enter an expression, in terms of defined variables, for the stress, S, that each nail will need to sustain at a temperature Ts.
b) What is the value of the stress, in pascals, that develops due to a rise of temperature to 21ºC?
c) Assuming the nails have a cross-sectional area of A = 10-5 m2 all of which is perpendicular to the stress force from the bar, what is the force acting on each due to that temperature rise?
d) Do you think it is possible to prevent the bar from expanding using nails?

After a big snowfall, you take your favorite rocket-powered sled out to a wide field. the field is 195 m across, and you know that your sled accelerates at a rate of 3.65 m/s2 when the rocket is on. how much time will it take the sled to cross the field starting from rest, assuming the rocket is on the whole time?

Did the proton move into a region of higher potential or lower potential? did the proton move into a region of higher potential or lower potential? because the proton is a negative charge and it accelerates as it travels, it must be moving from a region of higher potential to a region of lower potential.because the proton is a negative charge and it accelerates as it travels, it must be moving from a region of lower potential to a region of higher potential.because the proton is a positive charge and it slows down as it travels, it must be moving from a region of higher potential to a region of lower potential.because the proton is a positive charge and it slows down as it travels, it must be moving from a region of lower potential to a region of higher potential.request answerpart bwhat was the potential difference that stopped the proton? express your answer with the appropriate units.î”v î” v = nothingnothingrequest answerpart cwhat was the initial kinetic energy of the proton, in electron volts? express your answer in electron volts.ki k i = nothing ev request answerprovide feedback

The motor m applies a time-varying force of f (200 t) n, where t is in seconds. box b with mass 200 kg starts from rest, and the coefficients of kinetic and static friction are 0.2 and us 0.3 the acceleration due to gravity is g 9.8 m/s2 b 300 a) find the time ' when the box starts to move. b) calculate the speed of the crate at 3 s c) calculate the power delivered by the motor at t 3 s