<< Chapter < Page Chapter >> Page >
The diagram has a black rectangle that is slightly longer than it is tall with three solid arrows pointing from the edge of the rectangle. An arrow pointing up is labeled 40 N. A same size arrow pointing down is labeled 40 N. The third arrow f about half the size of the other two is pointing toward the left.

The figure shows the forces exerted on a block that is sliding on a horizontal surface: the gravitational force of 40 N, the 40 N normal force exerted by the surface, and a frictional force exerted to the left. The coefficient of friction between the block and the surface is 0.20. The acceleration of the block is most nearly

  1. 1.0 m/s 2 to the right
  2. 1.0 m/s 2 to the left
  3. 2.0 m/s 2 to the right
  4. 2.0 m/s 2 to the left
Got questions? Get instant answers now!

Summary

  • Newton’s laws of motion can be applied in numerous situations to solve problems of motion.
  • Some problems will contain multiple force vectors acting in different directions on an object. Be sure to draw diagrams, resolve all force vectors into horizontal and vertical components, and draw a free-body diagram. Always analyze the direction in which an object accelerates so that you can determine whether F net = ma size 12{F rSub { size 8{"net"} } = ital "ma"} {} or F net = 0 size 12{F rSub { size 8{"net"} } =0} {} .
  • The normal force on an object is not always equal in magnitude to the weight of the object. If an object is accelerating, the normal force will be less than or greater than the weight of the object. Also, if the object is on an inclined plane, the normal force will always be less than the full weight of the object.
  • Some problems will contain various physical quantities, such as forces, acceleration, velocity, or position. You can apply concepts from kinematics and dynamics in order to solve these problems of motion.

Conceptual questions

To simulate the apparent weightlessness of space orbit, astronauts are trained in the hold of a cargo aircraft that is accelerating downward at g size 12{g} {} . Why will they appear to be weightless, as measured by standing on a bathroom scale, in this accelerated frame of reference? Is there any difference between their apparent weightlessness in orbit and in the aircraft?

Got questions? Get instant answers now!

A cartoon shows the toupee coming off the head of an elevator passenger when the elevator rapidly stops during an upward ride. Can this really happen without the person being tied to the floor of the elevator? Explain your answer.

Got questions? Get instant answers now!

Problem exercises

A flea jumps by exerting a force of 1 . 20 × 10 5 N size 12{1 "." "20" times "10" rSup { size 8{ - 5} } " N"} {} straight down on the ground. A breeze blowing on the flea parallel to the ground exerts a force of 0 . 500 × 10 6 N size 12{0 "." "500" times "10" rSup { size 8{ - 6} } " N"} {} on the flea. Find the direction and magnitude of the acceleration of the flea if its mass is 6 . 00 × 10 7 kg size 12{6 "." "00" times "10" rSup { size 8{ - 7} } " kg"} {} . Do not neglect the gravitational force.

10.2 m/s 2 , 4.67º from vertical size 12{"10" "." 2" m/s" rSup { size 8{2} } ", 4" "." "68"°" from vertical"} {}

Got questions? Get instant answers now!

Two muscles in the back of the leg pull upward on the Achilles tendon, as shown in [link] . (These muscles are called the medial and lateral heads of the gastrocnemius muscle.) Find the magnitude and direction of the total force on the Achilles tendon. What type of movement could be caused by this force?

Got questions? Get instant answers now!
An Achilles tendon is shown in the figure with two forces acting upward, one at an angle of plus twenty degrees, one at minus twenty degrees. F sub one, equal to two hundred newtons, is shown by a vector making an angle twenty degrees toward the right with the vertical, and F sub two, equal to two hundred newtons, is shown making an angle of twenty degrees left from the vertical.
Achilles tendon

A 76.0-kg person is being pulled away from a burning building as shown in [link] . Calculate the tension in the two ropes if the person is momentarily motionless. Include a free-body diagram in your solution.

An object of mass m is shown being pulled by two ropes. Tension T sub two acts toward the right at an angle of ten degrees above the horizontal. Another rope makes an angle fifteen degrees to the left of the vertical direction, and tension in the rope is T sub one, shown by a vector arrow. Weight w is acting vertically downward.

T 1 = 736 N size 12{T rSub { size 8{1} } ="736"" N"} {}

T 2 = 194 N size 12{T rSub { size 8{2} } ="194 N"} {}

Got questions? Get instant answers now!
A lady is being pulled away from a burning building using a rope. She is in the middle of the rope; her weight is shown by a vector acting vertically downward. Tension, T sub one, acts upward through the left side of the rope, making an angle of fifteen degrees with the vertical. Tension T sub two acts through the right side of the rope, making an angle of ten degrees above the positive x axis.
The force T 2 size 12{T rSub { size 8{2} } } {} needed to hold steady the person being rescued from the fire is less than her weight and less than the force T 1 size 12{T rSub { size 8{1} } } {} in the other rope, since the more vertical rope supports a greater part of her weight (a vertical force).

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics for ap® courses' conversation and receive update notifications?

Ask