10. Conservation of Energy

Solving Projectile Motion Using Energy

Multiple Choice
You are practicing jumping as far as you can. In one attempt, you run and leave the floor with 7 m/s directed at an unknown angle. What maximum height do you reach if your speed at that point is 5 m/s? Ignore air resistance.
Multiple Choice
A toy gun is mounted on a tabletop. It shoots a small plastic ball at $6.0 m / s$ . The ball leaves the toy gun at an angle of 24° above the horizontal, and a height of $83 cm$ above the ground. How fast is the ball travelling when it hits the ground? Use energy concepts.
Multiple Choice
Calvin uses a catapult to launch a foam football at Susie. If the ball leaves the catapult at a height of $2.0 m$ and is moving at $15 m / s$ when it strikes the ground (he missed), how fast was the football moving when it left the catapult? Ignore air resistance.
Multiple Choice
A spring-loaded toy gun shoots a $3.0 g$ plastic ball straight up into the air. From the position of the ball when the gun is cocked, with the spring compressed, to the maximum height the ball reaches, is $2.5 m$ . If the spring was compressed $2.0 cm$ , what is the spring constant of the spring? Ignore air resistance.
Open Question
A film of Jesse Owens’s famous long jump (Fig. 8–48) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5 m/s at the top of the arc?
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Open Question
(III) Early test flights for the space shuttle used a “glider” (mass of 980 kg including pilot). After a horizontal launch at 480 km/h at a height of 3200 m, the glider eventually landed at sea level with a speed of 210 km/h.
(a) What would its landing speed have been in the absence of air resistance?