A box is being pulled by two ropes. Eduardo pulls to the left with a force of 500 N, and Clara pulls to the right with a force o
f 200 N. The box moves because of the two forces applied to it. Leon records the forces and direction of the forces acting on the box in his lab notebook. In the table, which force has the wrong direction?
Tension by Eduardo
Tension by Clara
Kinetic friction
Gravity
Tension by Eduardo
Tension by Clara
Kinetic friction
Gravity
2 answers:
Draw a diagram to illustrate the problem, as shown below.
m = mass of the box, kg
mg = weight of the box, N, acting downward
Because of Newton's 3rd law, a normal force of N = mg acts upward on the box.
C = 200 N, the force applied by Clara, horizontally to the right
E = 500 N, the force applied by Eduardo, horizontally to the left.
Because E is greater than C, the box will move left.
The frictional force, F, will resist the initial motion. Its magnitude is
F = μN = μmg, where μ = kinetic coefficient of friction.
F acts horizontally to the right.
From the given table, we can conclude that
Normal force acting upward is correct
Tension by Eduardoacting left is correct.
Tension by Clara acting right is correct.
Kinetic friction acting left is Incorrect.
Gravity acting downward is correct.correct
Answer:
The direction of the kinetic friction force is incorrect
m = mass of the box, kg
mg = weight of the box, N, acting downward
Because of Newton's 3rd law, a normal force of N = mg acts upward on the box.
C = 200 N, the force applied by Clara, horizontally to the right
E = 500 N, the force applied by Eduardo, horizontally to the left.
Because E is greater than C, the box will move left.
The frictional force, F, will resist the initial motion. Its magnitude is
F = μN = μmg, where μ = kinetic coefficient of friction.
F acts horizontally to the right.
From the given table, we can conclude that
Normal force acting upward is correct
Tension by Eduardoacting left is correct.
Tension by Clara acting right is correct.
Kinetic friction acting left is Incorrect.
Gravity acting downward is correct.correct
Answer:
The direction of the kinetic friction force is incorrect
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6.18 m/s
Explanation:
Roller skate collision
The final direction of the system (me=M + person=P) velocity vector is at an angle; Ф, to the direction running south to north. Apply the component form of the impulse-momentum equation, firstly;
x-axis component form (+x east);
+
+
=
+
Ф
60 ·8 + 0 = (60 + 80)Ф
480 = 140Ф................. (I)
y-axis component form (+y north);
+
+
=
+
Ф
0 + 80.9 = (60 + 80)Ф
720=
140Ф
140Vf=Ф......................................(2)
Substituting (2) into (1) to give the angle;
480 = 720tan Ф
Ф = arctan(0.67) =33.69°.......................(3)
Evaluating (1) with (3) gives the velocity magnitude
480 = 140Vfsin 33.69°
Vf=6.18 m/s
note 1:
This angle corresponds to a direction; 90° - 33.69° = 56.31° north of east.