1. Ch. 5 slides
Forces.ppt

2. Train accelerometer
A ball (mass m) hangs from a string (length L) inside a train car. The train car is moving forward with a constant acceleration, a0.
For the ball
draw a free-body diagram with axes indicated. What is the direction of the acceleration vector for the ball?
if possible, find the relationship between , a0, m, and g.
Forces.ppt

3. Barry Pushes Box
Barry pushes a 2000 Newton box at a steady 4 m/s along a horizontal wooden floor. If Barry pushes on the box with a 150 Newton force in a direction 30° below the horizontal, what is the force of friction on the box (include a motion diagram, identify the forces, and draw a free body diagram on your way to the solution)?
Forces.ppt

4. Block on Incline similar to Problem 5-16
A 1000 Newton box sits on a wooden incline. The incline makes a 30 °angle with the horizontal. What friction force will keep the box from sliding (include a motion diagram, identify the forces, and draw a free body diagram on your way to the solution)?
Forces.ppt

5. Push block similar to Problem 5-39 a)
Barry applies a horizontal force to a 6 kg wooden block resting on the floor. The coefficients of friction between the block and the floor are µk = 0.20 and µs = 0.5.
What is the minimum force that will cause the block to move?
What is the acceleration of the block if a 60 N force is applied to the block?
Forces2.ppt

6. Block on Incline 1
A block of mass 2 kg is placed on a 20° incline. Does the block slide down the incline? If so, calculate the acceleration.
Forces2.ppt

7. Block on Incline 2
A block of mass 2 kg is placed on a 30° incline and given a push, so it starts with a velocity of 1 m/s down the ramp. How fast is the block going at the end of the 2 m long ramp?
Forces2.ppt

8. Quick Stop
A car traveling at 20 m/s stops in a distance of 50 m. Assume that the deceleration is constant. The coefficients of friction between a passenger and the seat are µs = 0.5 and µk = 0.3. Will a 70 kg passenger slide off the seat if not wearing a seat belt? Justify your answer.
Forces2.ppt

9. Scales in Elevators
A 50 kg student gets in a 1000 kg elevator at rest. As the elevator begins to move, she has an apparent weight of 600 N for the first 3 s.
Is her apparent weight bigger or smaller than her regular weight?
Draw a Free Body Diagram for the student
How far has the elevator moved, and in which direction, at the end of 3 s?
Forces2.ppt

10. A large block
A large block (m1) is initially at rest on a frictionless surface. A second block (mass m2) slides off a table onto the top of the first with an initial speed v0. There is friction between the blocks with coefficients of friction µs and µk. The mass m1 is greater than m2.
a) Draw a free body diagram for each block and link any 3rd law pairs with a dotted line.
b) Which acceleration should be larger? Explain your reasoning.
c) Find the acceleration of each block in terms of m1, m2, µk, µs, and g.
Forces3rd3.ppt

11. Block over ledge
Block B (mB) sits on rough surface and is connected to block A (mA) by a massless string, as shown. The coefficients of friction between block B and the surface are µs and µk. Find the acceleration of the blocks (assuming they slide).
Draw a free body diagram for block A and block B.
Write out Newton’s 2nd law component equations for each block in terms of the forces you have defined on your free body diagram, mA, mB, aB, and aA. No numbers yet. There should be at least 3 equations.
Write down any constraining equations.
Find the value of a in terms of some combination of µk, µs, mA, mB, and g.
Given that mA = 1 kg. mB = 2 kg, µs = 0.8, and µk = 0.2, find the numerical value of a.
What is the minimum value of mA that will cause the blocks to slip if the blocks start at rest?
Forces3rd3.ppt

12. Two blocks being pushed
Two blocks (m1 = 3 kg and m2 = 1 kg) are in contact on a frictionless table. A horizontal force of 4 N is applied to m1, as shown below.
a) Find the acceleration of the blocks.
b) Find the force between the two blocks.
The force is now applied to m2 in the opposite direction.
c) Will the magnitude of the acceleration change?
d) Find the force between the two blocks? (It's not the same as before.
e) Explain why the force between the two blocks is different in the above cases.
Forces3rd3.ppt