The answer is right. The point and the 200 N sign maybe on the left side but the direction can be going right. I just took the quiz today, I wouldn't give the wrong answer cause i'm not a liar. -_-
Answer:
vf = v₁/3 + 2v₂/3
Explanation:
Using the law of conservation of linear momentum,
momentum before impact = momentum after impact
So, Mv₁ + 2Mv₂ = 3Mv (since the railroad cars combine) where v₁ = initial velocity of first railroad car, v₂ = initial velocity of the other two coupled railroad cars, and vf = final velocity of the three railroad cars after impact.
Mv₁ + 2Mv₂ = 3Mvf
dividing through by 3M, we have
v₁/3 + 2v₂/3 = vf
vf = v₁/3 + 2v₂/3
Answer : The half-life of this substance will be, 45 minutes.
Explanation :
First we have to calculate the value of rate constant.
Expression for rate law for first order kinetics is given by:

where,
k = rate constant = ?
t = time passed by the sample = 90.3 min
a = initial amount of the reactant = 400
a - x = amount left after decay process = 100
Now put all the given values in above equation, we get


Now we have to calculate the half-life of substance, we use the formula :



Therefore, the half-life of this substance will be, 45 minutes.