Physics Review

Newton's Laws

100

A person who weighs 800N steps on a scale on the floor of an elevator. If the elevator accelerates upward at 5m/s² what will the scale read?

a. 400N

b. 800N

c. 1000N

d. 1200N

d

200

The planet mars exerts a gravitational force F_mars on its moon. The moon has a smaller than Mars and exerts a gravitational force F_moon on Mars. Which statement is true?

a. F_mars>F_moon

b. F_moon>F_mars

c. F_mars=F_moon

c

300

A block is pushed along a horizontal and frictionless surface with a horizontal force that varies as a function of time. At t=3s, the acceleration of the block is 5m/s² and the force is 15N. What is the mass of the block?

a. 1kg

b. 2kg

c. 3kg

d. 5kg

c

400

An artificial satellite of mass m1 = 400 kg orbits the earth at a distance

r = 6.45 x 10⁶ m above the center of the earth. The mass of the earth is m2 = 5.98 x 10²⁴ kg. Find (a) the weight of the satellite and (b) the acceleration due to gravity at this orbital radius.

a. 3835N

F_g=(Gm₁m₂)/r²

Fg₌(6.67x10^-11)(400)(5.98x10²⁴)

b. 9.59m/s²

F=ma

3835/400

500

An elevator cable supports an empty elevator car of mass 300 kg. Determine the tension in the cable when the elevator car is (a) at rest and (b) the car has a downward acceleration of 2.0 m/s².

 

a. When the elevator car is at rest, the tension in the cable FT is equal to the weight W of the car:

 

FT = W = mg = (300 kg)(10 m/s2) = 3000 N.

(b) When the elevator car is being lowered with an acceleration of 2.0 m/s2, the downward weight force is greater than the upward tension force. We can use Newton’s second law to find the tension in the cable. Choosing the downward direction as positive,

F=MA

(W-F_T)=ma

(3000)-(300)(2)

2400N upward

Electrostatics

100

What is the direction of electric field lines on a positive charge? On a negative charge? 

a. Away from a positive charge & towards a negative charge

b. towards a positive charge & away from a negative charge

c. away from both positive & negative charges

d. towards both positive & negative charges

a

200

What is coulombs law?

F=(kq₁q₂)/r²

300

Determine the electrical force of attraction between 2 balloons that are charged with the opposite type, but same quantity of charge. The charge is 6x10^-7 C and the distance between the balloons is .5m.  

F=1.3x10^-2N

400

Two point charges, each having a charge of +1C, are 2 meters apart. If the distance between them is doubled, by what factor does the force between them change?

k=9.0×10⁹N⋅m²/C²

1/4 

explanation: 

F_e=kq₁q₂/r²

r_f=2r_i

500

A point charge of magnitude 1.6∗10⁻⁵C is located 0.01m away from a point charge of magnitude 2∗10⁻⁵C. What is the electric force between the point charges?

k=9∗10⁹N⋅m²C²

28800N

F=9∗10⁹∗1.6∗10⁻⁵∗2∗10⁻⁵/0.01²

Rotational Motion

100

What is the equation for torque?

T = r F sin θ

200

A wheel spinning at 3 m/s uniformly accelerates to 6 m/s in 4 s. Its radius is 20 cm. How far around the wheel will a speck of dust travel during that interval?

A) 6 m B) 18 m C) 9 m D) 30 m E) 12 m

Ans. 𝑎 = 𝑣 −𝑣𝑜 𝑡 = 6 𝑚 𝑠 −3 𝑚 𝑠 4 𝑠 = ¾ m/s2 v 2 = vo 2 + 2ax (6 m/s)2 = (3 m/s)2 + 2(¾ m/s2 )x 36 = 9 + 3/2x 27 = 3/2x 18 m

B) 18 m

300

A bicycle moves at constant speed over a hill along a smoothly curved surface as shown above. Which of the following best describes the directions of the velocity and the acceleration at the instant it is at the highest position? 

A) The velocity is towards the right of the page and the acceleration is towards the top of the page. 

B) The velocity is towards the right of the page and the acceleration is towards the bottom of the page. 

C) The velocity is towards the right of the page and the acceleration is towards the bottom right of the page

B) The velocity is towards the right of the page and the acceleration is towards the bottom of the page.

400

A solid cylinder with diameter 20 cm has an angular velocity of 10 rad/s and angular momentum of 2 kg  x m2 /s. What is its mass?

A) 0.1 kg B) 5 kg C) 1 kg D) 10 kg E) 2 kg

10 kg

500

A bowling ball of mass 6.0 kg is released from rest from the top of a slanted roof that is 4,0 m long and angled at 30 degrees. The ball rolls along the roof without slipping. The rotational inertia of a sphere of mass M and radius R about its center of mass is 2/5 MR².

a) Calculate the force due to friction acting on the ball as it rolls along the roof.

b) Calculate the linear speed of the center of mass of the ball when it reaches the bottom edge of the roof.

a) 8.6 N

b) 5.34 m/s

Gravity

100

At earth's surface what is the acceleration of gravity?

9.8 m/s^2

200

A block with a mass of 10kg is traveling at 50m/s when it impacts the ground. From how many meters off the ground was the block dropped?

a. 126m

b. 128m

c. 124m

d. 130m

b. 128

300

A ship of mass m and an initial velocity of v0 is coasting to a stop. The water exerts a drag force on the ship. The drag force is proportional to the velocity:

FD=−kv where the negative sign indicates that the drag force acts in a direction opposite the motion. After the ship has coasted for a time equal to 2/k, how fast (in terms of v0) will the ship be moving?

a. 0.37v0

b. 0.63v0

c. 0.135v0

c. 0.135v0

400

With what minimum velocity must a rocket be launched from the surface of the moon in order to not fall back down due to the moon's gravity?

The mass of the moon is 7.2∗1022kg and its radius is 1.8∗106m.

G=6.67∗10−11m^2N/kg2

a. 2.3km/s

b. 470m/s

c. 520m/s

d. 1.6km/s

a. 2.3km/s

500

A 100kg satellite is in a Earth circular orbit with radius 1.2 x 10^7 m.

Find the speed.

5,765 m/s