(a) a runaway train car that has a mass of 14000 kg travels at a speed of 7.5 m/s down a track. compute the time (in seconds) required for a force of 1400 n to bring the car to rest. s (5 attempts remaining) input 1 status (b) a bullet is accelerated (from rest) down the barrel of a gun by hot gases produced in the combustion of gun powder. if the average force exerted on a 0.023 kg bullet to accelerate it is 3700 n, what will be the bullet's speed (in m/s) in a time of 0.002 s

In the picture.

Explanation:

I hope that it's a clear solution and explanation.

a) There is 75s needed for a force of 1400N to bring to car to rest.

b) The bullet's speed will be 321.74 m/s

Explanation:

a) Step 1: Given data:

Mass = 14000kg

speed (v0) = 7.5m/s

1400N needed to bring the car to rest ( means v= 0) (The force will be negative since it's in the opposite direction

Step 2: Newton's law

∑F = m * a   OR

a = ∑F / m

a = -1400N / 14000kg = -0.1 m/s²

Step 3: Calculate the time needed

v = v0 + at   OR

t = (v- v0)/ a

t = (0 - 7.5) / -0.1 = 75 s

There is 75s needed for a force of 1400N to bring to car to rest.

b)

Step 1: Given data

mass = 0.023kg

force = 3700N

time = 0.002s

Step 2: Calculate impulse

ΔP = 3700N * 2 ms = 7.4 Ns

Step 3: Calculate speed

Impulse ΔP = m(v-v0)    since v0 = 0 we can write this formula as:

ΔP = m*v

v= ΔP / m

v= 7.4 Ns / 0.023kg = 321.74 m/s

The bullet's speed will be 321.74 m/s

no. dot product   =0 when vecs at right angles

does anyone know or what?