Physics question of the week (2)

A 1750 kg truck is heading east at 15 m/s when it collides with a 1300 kg car traveling
west. After the collision the car and truck are stuck together and slide west at 4.0 m/s.

a)What was the initial velocity of the car?
b) What was the impulse felt by the truck?
c) Was this collision elastic or inelastic?

Math question of the week (3)

When John throws a stone at a target, the probability that he hits the target is 0.4 He throws a stone 6 times. 

(a) Find the probability that he hits the target exactly 4 times. 

(b) Find the probability that he hits the target for the first time on his third throw.

Answer key for Math question (2)

a) 7C4 [ (0.9)^4 * (1 - 0.9)^(7 - 4) ] 
     = 7!/(4!*3!) [(0.9)^4 * (0.1)^3] 
     = 35(0.0006561) 
        =0.023

b) 7C4 [p^4 * (1 - p)^3] 
     = 35p^4(1 - 3p + 3p^2 - p^3) 
     = 35p^4 - 105p^5 + 105p^6 - 35p^7

c) 0.15 = 35p^4 - 105p^5 + 105p^6 - 35p^7
    p = 0.356 or

    p = 0.770

Answer key for physics question (1)

(a) R = v /I = 120 / 0.25 = 480 Ω


(b) P = IV = (0.25)(120) = 30 w


(c) I = q / t ; q = (0.25)(15) = 3.75 C


     (3.75)(1 / 1.6 x 10^-19) = 2.34 x 10^-19  e^-

Math question of the week (2)

Evan likes to play two games of chance, A and B.

For game A, the probability that Evan wins is 0.9. He plays game A seven times.

(a) Find the probability that he wins exactly four games. 

     For game B, the probability that Evan wins is p . He plays game B seven times.

(b) Write down an expression, in terms of p , for the probability that he wins exactly

     four games. 

(c) Hence, find the values of p such that the probability that he wins exactly four

     games is 0.15.