Physics

Week 3 Homework

Chapter 5 page 143

1. A crate of mass 6.00 kg is moved by a force of 18.0 N. What is its acceleration?

a= f/m

a= 18.0 N / 6.00 kg

a= 3 N/kg * 1 kg m/s^2

a= 3 m/s^2

7. A truck pulls a trailer with a frictional force of 870 N and a coefficient of friction of 0.23. What is the trailer’s normal force?

Fn= 870 N / 0.23

Fn= 3782.60 N

9. A rock of a mass 13.0 kg is dropped from a cliff. Find its weight.

m=13.0 kg g= 9.80 m/s^2

Fw= 13.0 kg * 9.80 m/s^2

Fw = 127.4 kg m/s^2

Fw = 127.4 N (1 N= 1kg m/s^2)

Fw = 127.4 N

13. A force of 175 N is needed to keep a 640¯-N stationary engine on wooden skids from sliding on a wooden floor. What is the coefficient of static friction?

Ff = 175 N Fn = 640- -N

μ = 175 N/ 640- -N

μ = 175 N / 640 N

μ = 0.2734375 = 0.273

15. Find the acceleration of a forklift of mass 140¯0 kg pushed by a force of 210¯0 N that is opposed by a frictional force of 425 N.

2100 N – 425 N = 1675 N

a= f/m

a= 1675 N / 1400kg

a= 1.96 N/kg * (1m/s ^2 / 1kg)

a= 1.196 m/s^2 = 1.20 m/s^2

Chapter 6 page 163

2. A box is pushed with a force of 125 N for 2.00 min. What is the impulse?

Impulse = Ft

Impulse = 125 N * 2.00 min

Impulse = 125 N *120 s

Impulse = 15,000 N

7. A 15.0-g bullet is fired at a muzzle velocity of 3250 m/s from a high-powered rifle with a mass of 4.75 kg and barrel of length 75.0 cm. (a) How long is the bullet in the barrel? (b) What is the force on the bullet while it is in the barrel? (c) Find the impulse exerted on the bullet while it is in the barrel. (d) Find the bullet’s momentum as it leaves the barrel.

A. How long is the bullet in the barrel?

S = 75.0 cm = 0.750m

Vf = 3250 m/s

Vi = 0 m/s

Vavg = (3250 m/s + 0 m/s) / 2 = 1625 m/s

t= 0.750 m / 1625 m/s = 0.0000462 s

t= 4.62 x 10^-5 s

B. What is the force on the bullet while it is in the barrel?

t= 0.0000461538 s

m= 15.0g = 0.015 kg

Vf= 3250 m/s

Vi= 0 m/s

F= (0.015kg)(3250 m/s) –...