1. Mary pulls on a lawnmower parallel to the ground
Mary pulls on a lawnmower parallel to the ground. The mower moves at a constant speed up the hill.
Which free body diagram best represents the forces on the mower? x y x y 2 1 x y 3 x y 4

2. 1 2 4 3 Stacey pulls a mower at 40-degrees relative to the ground.
Which free body diagram best represents the forces on the mower? x
400 y y x
400 1 2 4 3 y x
400 x y
400

3. x: (150 N) = (45 kg) ax y: N – (45 kg)(10 m/s2) = (45 kg) 0
Marsha pulls a sled on ice (no friction). The rope exerts a 150-N force at an angle of 200 above horizontal. The mass of the sled and her brother is 45 kg. g = 10 m/s2. Stacey represented this situation pictorially and mathematically. x
x: (150 N) = (45 kg) ax
y: N – (45 kg)(10 m/s2) = (45 kg) 0
Did the student mislabel or forget to include anything?
1 (150 N) should be
(150 N) sin 20o.
2 (150 N) should be
(150 N) cos 20o.
3 Include a +(150 N) sin 20o term in the y equation.
4 Both (1) and (3) need corrections.
5 Both (2) and (3) need corrections.

4. What are the missing signs?
Steve pulls a sled on ice (no friction) with a 150-N force at an angle of The mass of the sled and her brother is 45 kg. g = 10 m/s2. Stacey represented this pictorially and mathematically. x o
x: (150 N) cos 20o = (45 kg) ax
y: __ N __ (45 kg)(10 m/s2) __ (150 N) sin 20o = 0
What are the missing signs?
1 + – +
2 + + –
3 – – +
4 – – –

5. The motion of a car is represented with the motion diagram below.x o
Which diagram best represents the forces exerted on the car by the Earth and the Earth’s surface? x y 1 x y 2 x y 3 4 y x y 5 x

6. x: 0 – (0.80 N) = (1000 kg) ax y: N – (1000 kg)(10 m/s2) = (1000 kg) 0
0 – 16 m/s = ax t
Which word description below best matches the above mathematical description?
The 0.80 N force of the Earth on the object causes its speed in the x direction to increase from 0 to 16 m/s.
The object slows down due to a 0.80 N frictional force.
The object has a 10 m/s2 acceleration in the y direction.
The net force causing the object to slow down is exerted in the same direction as the initial velocity.
5 The object’s velocity increases from 0 to 16 m/s.

7. Which FBD best represents the above motion diagram for a car?x y 1 2 y x x y 3 x y 4

8. Which motion diagram best represents the situation shown in the free-body diagram?2 1 4 3
5 Either 2 or 4 are possible

9. Which FBD below best represents the forces exerted on the ball as it moves UP (ignore air resistance)? 1 2 3 4

10. Which FBD below best represents the forces exerted on the ball as it moves DOWN (ignore air resistance)? 1 2 3 4

11. Which FBD below best represents the forces exerted on the ball at the TOP of its path?2 1 4 3
5 No forces are exerted on the ball

12. x y
Which motion diagram best represents the situation as shown by the free-body diagram? 2 1 4 3
5 No diagram -- the stroller must be accelerating to the right because the net force is to the right.

13. Which speed versus time chart best represents this situation?y x
Which speed versus time chart best represents this situation? 1 2 3 v v v t t t