# physics

1) What average power is required for a runner with a mass of 85 kg to reach a speed of 8 m/s from
a stationary start during a time of 2 s?

2) A 1000 kg car travels east at 30 m/s and collides with a 3400 kg truck travelling south at 20 m/s.
After the collision the two vechicles remain stuck together.
(a) What is the total initial momentum of the car truck system?
(b) What is the total final momentum of the car truck system?
(c) In what direction are the car and truck moving after the collision?
(d) Immediately after the collision how fast are the car and truck moving?
(e) How much kinetic energy is lost in this collision? Where does this energy go?

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1. 1. P = Mg * Vavg = 85*9.8 * 8/2 = 3332 J/s = 3332 Watts

2a. Momentum = M1*V1 + M2*V2 =
1000*30 + 3400*20i = 30,000 - 68,000i,Q4
= sqrt(30,000^2+68000^2) = 74,324 kg-m/s

2b. Total final momentum = Total initial
momentum = 74,324 kg-m/s.

2c. M1*V1 + M2*V2 = M1*V + M2*V
30,000 - 68000i=1000*V + 3400*V = 4400V
4400V = 74324[-66.2o]
V = 16.9 m/s[-66.2o] = 16.9 m/s at 66.2o
S. of E.

2d. V = 16.9 m/s(Part 2c).

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posted by Henry

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