19. Answer: D. A car moving northeast at 90 km/hr
To answer this question you have to know the difference between velocity and speed. Velocity is the same as speed, but with direction. Option A and option B doesn't even have speed as it don't give a distance per time unit. Option C have speed, but doesn't have direction so it doesn't have velocity.
20. Answer: C. Accel 1 has a constant rate of acceleration; Accel 2 accelerates at different rates during the trip.
The velocity graph of Accel 1 is an upward straight line. This show that the velocity keep increasing through the entire trip, so it should have constant positive acceleration the entire trip.
The velocity graph of Accel 2 start with higher upward straight line, but then downward until zero. This show there is a positive acceleration on the first trip, but then become negative at the end. There is a change in the Accel 2 acceleration.
21. Answer: C) 200 N right
From the picture, the object has 50N downward force, 50N upward force and 200N force to the right.
The sum of the force in vertical direction would be: 50N- 50N=0N.
The sum of the force in horizontal direction would be: 200N.
The answer will be 200N to the right
22. Answer: d) a toy car moving east at a constant velocity
When the net force of an object is greater than zero, the force will be converted into kinetic energy which will increase the velocity the object. This will allow the object to have acceleration. A glass resting and a ladder leaning against a wall doesn't even have velocity. A toy car moving east at a constant velocity, doesn't have acceleration.
23. Answer: B. increases.
Gravity cause the object to have potential energy. Gravity force is directly related to the mass and inversely related to the distance square of the object. If the mass increases, then potential energy of the object would be increased too.
24. C. The part will move at a constant speed along a straight path until it is acted upon by another force.
The part get energy from the astronaut force which converted into kinetic energy. As long as the part having kinetic energy, it will continually move. Since the space has no air, there will be no air to stop the part. The part will continue to move at constant speed(no acceleration) until any force bump into it.
25. Answer: D. The hockey stick will change the speed of the puck and make it accelerate.
If an object collide with another stationary object, some of the kinetic energy will be transferred. The kinetic energy of the hockey stick will be transferred to the puck, which cause the puck to have acceleration. The hockey stick will lose some energy and become a bit slower because of this.
26. Answer: D. For every action your cat makes, there is an equal and opposite reaction from the string.
This case is similar to the previous question. When the cat moving her paw and collide with the toy(action), there will be some force put on both the toy and cat paw. The force will cause the toy accelerate and make it moving away from the cat(reaction) while reducing the kinetic energy of the cat paw.
27 Answer: B. They hit each other with the same force in opposite directions.
This will also be explained by Newton's third law of motion. For every action there will be equal opposite reaction. When baseball and bat collide, the action from baseball will cause reaction on the bat and the baseball. The action from the bat also will cause reaction on the bat and the baseball too.
