Slide 1 / 76 Work & Energy Multiple Choice Problems Slide 2 / 76 1 A driver in a 2000 kg Porsche wishes to pass a slow moving school bus on a 4 lane road. What is the average power in watts required to accelerate the sports car from 30 m/s to 60 m/s in 9 seconds? A 1,800 B 5,000 C 10,000 D 100,000 E 300,000 Slide 3 / 76 2 A force F is at an angle θ above the horizontal is used to pull a heavy suitcase of weight mg a distance d along a level floor at constant velocity. The coefficient of friction between the floor and the suitcase is μ. The work done by the force F is: A Fdcos θ - μ mgd B Fdcos θ C -μ mgd D 2Fdsin θ - μ mgd E Fdcos θ - 1
Slide 4 / 76 3 A force of 20 N compresses a spring with spring constant 50 N/m. How much energy is stored in the spring? A 2 J B 5 J C 4 J D 6 J E 8 J Slide 5 / 76 4 A stone is dropped from the edge of a cliff. Which of the following graphs best represents the stone's kinetic energy KE as a function of time t? C A B D E Slide 6 / 76 A 4 kg ball is attached to a 1.5 m long string and 5 whirled in a horizontal circle at a constant speed of 5 m/s. How much work is done on the ball during one period A 9 J B 4.5 J C zero D 2 J E 8 J
Slide 7 / 76 6 A student pushes a box across a horizontal surface at a constant speed of 0.6 m/s. The box has a mass of 40 kg, and the coefficient of kinetic friction is 0.5. The power supplied to the box by the person is A 40 W B 60 W C 150 W D 120 W E 200 W Slide 8 / 76 A force F is applied in horizontal to a 10 kg block. 7 The block moves at a constant speed 2 m/s across a horizontal surface. The coefficient of kinetic friction between the block and the surface is 0.5. The work done by the force F in 1.5 minutes is: A 9000 J B 5000 J C 3000 J D 2000 J E 1000 J Slide 9 / 76 8 A ball swings from point 1 to point 3. Assuming the ball is in SHM and point 3 is 2 m above the lowest point 2. Answer the following questions. What happens to the kinetic energy of the ball when it moves from point 1 to point 2? A increases B decreases C remains the same D zero E more information is required
Slide 10 / 76 9 A ball swings from point 1 to point 3. Assuming the ball is in SHM and point 3 is 2 m above the lowest point 2. Answer the following questions. What is the velocity of the ball at the lowest point 2? A 2.2 m/s B 3.5 m/s C 4.7 m/s D 5.1 m/s E 6.3 m/s Slide 11 / 76 10 A block with a mass of m slides at a constant velocity V 0 on a horizontal frictionless surface. The block collides with a spring and comes to rest when the spring is compressed to the maximum value. If the spring constant is K, what is the maximum compression in the spring? V 0 (m/k) 1/2 A B KmV 0 C V 0 K/m D m V 0 /K V 0 (K/m) 1/2 E (V 0 m/K) 1/2 F Slide 12 / 76 11 A 2 kg block released from rest from the top of an incline plane. There is no friction between the block and the surface. How much work is done by the gravitational force on the block? A 80 J B 60 J C 50 J D 40 J E 30 J
Slide 13 / 76 12 A 2 kg block released from rest from the top of an incline plane. There is no friction between the block and the surface. What is the speed of the block when it reaches the horizontal surface? A 3.2 m/s B 4.3 m/s C 5.8 m/s D 7.7 m/s E 6.6 m/s Slide 14 / 76 13 A crane lifts a 300 kg load at a constant speed to the top of a building 60 m high in 15 s. The average power expended by the crane to overcome gravity is: A 10,000 W B 12,000 W C 15,000 W D 30,000 W E 60,000 W Slide 15 / 76 14 A satellite with a mass m revolves around Earth in a circular orbit with a constant radius R. What is the kinetic energy of the satellite if Earth’s mass is M? A ½ mv B mgh ½GMm/R 2 C D ½ GMm/R E 2Mm/R
Slide 16 / 76 15 An apple of mass m is thrown in horizontal from the edge of a cliff with a height of H. What is the total mechanical energy of the apple with respect to the ground when it is at the edge of the cliff? 2 A 1/2mv 0 B mgH 2 - mgH C ½ mv 0 2 D mgH - ½ mv 0 2 E mgH + ½ mv 0 Slide 17 / 76 16 An apple of mass m is thrown in horizontal from the edge of a cliff with a height of H. What is the kinetic energy of the apple just before it hits the ground? 2 + mgH A ½ mv 0 2 - mgH B ½ mv 0 C mgH 2 D ½ mv 0 2 E mgh - 1/2 mv 0 Slide 18 / 76 17 A 500 kg roller coaster car starts from rest at point A and moves down the curved track. Ignore any energy loss due to friction. Find the speed of the car at the lowest point B. A 10 m/s B 20 m/s C 30 m/s D 40 m/s E 50 m/s
Slide 19 / 76 18 A 500 kg roller coaster car starts from rest at point A and moves down the curved track. Ignore any energy loss due to friction. Find the speed of the car when it reaches point C. A 10 m/s B 20 m/s C 30 m/s D 40 m/s E 50 m/s Slide 20 / 76 19 Two projectiles A and B are launched from the ground with velocities of 50 m/s at 60 ̊ and 50 m/s at 30 ̊ with respect to the horizontal. Assuming there is no air resistance involved, which projectile has greater kinetic energy when it reaches the highest point? A projectile A B projectile B they both have the same none zero kinetic C energy they both have zero kinetic energy at the D highest point E more information is required Slide 21 / 76 20 An object with a mass of 2 kg is initially at rest at a position x = 0. A non-constant force F is applied to the object over 6 meters. What is the total work done on the object? A 200 J B 150 J C 170 J D 190 J E 180 J
Slide 22 / 76 21 An object with a mass of 2 kg is initially at rest at a position x=0. A non-constant force F is applied to the object over 6 meters. What is the velocity of the object at 6 meters? 150 m/s A B 25 m/s C 300 m/s D 12.25 m/s E not enough information Slide 23 / 76 22 A metal ball is held stationary at a height h 0 above the floor and then thrown upward. Assuming the collision with the floor is elastic, which graph best shows the relationship between the total energy E of the metal ball and its height h with respect to the floor? B C A D E Slide 24 / 76 23 A toy car travels with speed v o at point x. Point Y is a height H below point x. Assuming there is no frictional losses and no work is done by a motor, what is the speed at point Y? 2 ) 1/2 A (2gH+1/2v o B v o -2gH 2 ) 1/2 C (2gH + v o 2 ) 1/2 D 2gH+(1/2v o E v o +2gH
Slide 25 / 76 24 A rocker is launched from the surface of a planet with mass M and radius R. What is the minimum velocity the rocket must be given to completely escape from the planet's gravitational field? A (2GM/R) 1/2 B (2GM/R) 1/2 C (GM/R) 1/2 D 2GM/R E 2GM/16R 2 Slide 26 / 76 25 A block of mass m is placed on a frictionless inclined plane with an incline angle θ. The block is just in contact with a free end of an unstretched spring with a spring constant k. If the block is released from rest, what is the maximum compression in the spring? A kmg sin θ B kmg cos θ C 2mg sin θ /k D mg/k E kmg Slide 27 / 76 In a physics lab a student uses three light 26 frictionless PASCO lab carts. Each cart is loaded with some blocks, each having the same mass. The same force F is applied to each cart and they move equal distances d. In which on of these three cases is more work done by force F? A cart I B cart II C cart III the same work is done D on each E more information is required
Slide 28 / 76 In a physics lab a student uses three light 27 frictionless PASCO lab carts. Each cart is loaded with some blocks, each having the same mass. The same force F is applied to each cart and they move equal distances d. Which cart will have more kinetic energy at the end of distance d? A cart I B cart II C cart III all three will have the D same kinetic energy E more information is required Slide 29 / 76 In a physics lab a student uses three light 28 frictionless PASCO lab carts. Each cart is loaded with some blocks, each having the same mass. The same force F is applied to each cart and they move equal distances d. Which cart will move faster at the end of distance d? A cart I cart II B C cart III all three will move D with the same speed E more information is required Slide 30 / 76
Slide 31 / 76 30 A ball of mass m is fastened to a string. The ball swings in a vertical circle of radius r with the other end of the string held fixed. Neglecting air resistance, the difference between the string's tension at the bottom of the circle and at the top of the circle is: A mg B 2mg C 3mg D 6mg E 9mg Slide 32 / 76 Work & Energy Free Response Problems Slide 33 / 76 1. A 50 kg block is pulled from rest by a force of 1000 N at 37° across a horizontal rough surface over a distance of 5.6 m. The coefficient of kinetic friction between the block and the surface is 0.5. a. Draw a free-body diagram and show all the applied forces. b. How much work is done by force F? c. How much work is done by the normal force? d. How much work is done by the gravitational force? e. How much work is done by the friction force? f. What is the net work done on the block? g. What is the change in kinetic energy of the block?
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