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

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

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.

What are the missing signs? Steve pulls a sled on ice (no friction) with a 150-N force at an angle of 200. 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

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.

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

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

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

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

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

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.

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