Question

Find the speed [km/h] at which Superman (mass=85 kg) must fly into a train (mass = 19000 kg) traveling at 77 km/hr to stop it?

A: 1.38×104

B: 1.72×104

C: 2.15×104

D: 2.69×104

E: 3.36×104

Tries 0/1

Running into the train at that speed would severely damage both train and passengers.
Calculate the minimum time [s] Superman must take to stop the train, if the passengers experience an average acceleration of -0.44*g (g = 10 m/s²)?

A: 1.59

B: 2.31

C: 3.35

D: 4.86

E: 7.05

Tries 0/1

How far [m] does the train then travel while being slowed to a stop?

A: 38.0

B: 44.4

C: 52.0

D: 60.8

E: 71.2

Answer 1

A)

The linear momentum remains conserved

The momentum of the system before collision = momentum of the system after collision.

(After collision the velocity of train as well as superman is zero because both is zero)

So minus only represent the direction opposite

B)

We know that, according to the first equation of motion,

t = 4.86 sec

C)

To find the distance, we need to consider third equation of motion

s = 51.98 = 52 m