Question

1. A car accelerates from 32km/hr to 65 km/hr over 200m. What is the magnitude of the force acting on it? Assume the car has a mass if 980 kg

2. Justin just does not have it anymore. He demands to throw a fast ball but his catcher says to throw a curve because his fast ball is not fast enough. Justin insists to throw a fast ball and does. His catcher takes off his glove and catches the ball bare handed.
a. Determine the impulse required to stop a 0.153-kg baseball moving at 25.7m/s (3 points)






b. If this impulse is delivered to the ball in 0.015 seconds, then what is magnitude of the force acting between the bare hand and the ball? (2 points)


3. A 102 kg bungee jumper jumps off a bridge on Mars. The bridge is 405 m above the river at its center point. The bungee cord spring constant is 44 N/m, the cords relaxed length is 130 m and its length is 235 m when the jumper stops falling. What is the T

Answer 1

#1

As per kinematics we know that

`v_f^2 - v_i^2 = 2 a s`

here we know that

`v_f = 65 km/h = 18.1 m/s`

`v_i = 32 km/h = 8.9 m/s`

`s = 200 m`

now we will have

`18.1^2 - 8.9^2 = 2(a)(200)`

`a = 0.62 m/s^2`

Now by Newton's II law

`F = ma`

`F = 980 * 0.62 = 608.6 N`

#2

part a)

Impulse = change in momentum

`I = m(v_f - v_i)`

given that

m = 0.153 kg

v = 25.7 m/s

now we have

`I = 0.153(25.7 - 0) = 3.93 kg m/s`

Part b)

As per Newton's II law we know that

`F = (\Delta P)/(\Delta t) = (I)/(\Delta t)`

as we know that

`\Delta t = 0.015 s`

`F = (3.93)/(0.015) = 262.14 N`