I\'m hoping that someone could give me the solution to some physics problems tha

Question

I'm hoping that someone could give me the solution to some physics problems that I have been having problems with. 1. A boy throws a rock off a bridge with a velocity of 15 m/s at an angle of 30 degrees above the horizontal. If the rock strikes the water after 3.5 seconds, how far does the rock travel in the horizontal direction before striking the water and how high is the bridge? 2. A car of mass 2000 kg moving at 30 m/s is braked suddenly. How far does it travel before stopping if the coefficient of kinetic friction between the tires and the pavement is 0.55? Thanks for the help!

Explanation / Answer

1) Horizontal velocity = 15*cos(30) = 12.99 m/sec

Distance travelled = velocity*time = 12.99*3.5 = 45.46 m

2) Frictional force = mu*m*g = 0.55*2000*9.81 = 10791 N

acceleration(retardation) = F/m = 10791/2000 = 5.395 m/sec^2

u^2 = 2*a*s

s = u^2 / (2*a) = 30^2 / (2*5.395) = 83.4 m

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