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A ball is thrown vertically upwards. Air resistance is negligible. What is the variation with time t of the kinetic energy Ek of the ball?
ANSWER: D
The tension in a horizontal spring is directly proportional to the extension of the spring. The energy stored in the spring at extension x is E. What is the work done by the spring when its extension changes from x to x/4?
ANSWER: D
An object of mass m is sliding down a ramp at constant speed. During the motion it travels a distance x along the ramp and falls through a vertical distance h. The coefficient of dynamic friction between the ramp and the object is μ. What is the total energy transferred into thermal energy when the object travels distance x?
A. mgh
B. mgx
C. μmgh
D. μmgx
ANSWER: A
An object has a weight of 6.10 × 10^2 N. What is the change in gravitational potential energy of the object when it moves through 8.0 m vertically?
A. 5 kJ
B. 4.9 kJ
C. 4.88 kJ
D. 4.880 kJ
ANSWER: B
A boat with an output engine power of 15 kW moves through water at a speed of 10 m s^-1. What is the resistive force acting on the boat?
ANSWER: 1.5 kN
A compressed spring is used to launch an object along a horizontal frictionless surface. When the spring is compressed through a distance x and released, the object leaves the spring at speed v. What is the distance through which the spring must be compressed for the object to leave the spring at v/2?
ANSWER: B
An object falls from rest from a height h close to the surface of the Moon. The Moon has no atmosphere. When the object has fallen to height h/4 above the surface, what is: Kinetic energy of the object at h/4 OVER gravitational potential energy of the object at h?
ANSWER: A
An increasing force acts on a metal wire and the wire extends from an initial length l₀ to a new length l. The graph shows the variation of force with length for the wire. The energy required to extend the wire from lo to l is E. The wire then contracts to half its original extension. What is the work done by the wire as it contracts?
ANSWER: 0.75E
A motor of input power 160 W raises a mass of 8.0 kg vertically at a constant speed of 0.50 m s^–1. What is the efficiency of the system?
ANSWER: 25%
A system that consists of a single spring stores a total elastic potential energy Ep when a load is added to the spring. Another identical spring connected in parallel is added to the system. The same load is now applied to the parallel springs. What is the total elastic potential energy stored int he changed system?
ANSWER: B
A graph shows the variation of force acting on an object moving in a straight line with distance moved by the object. Which area represents the work done on the object during its motion from P to Q?
A. X
B. Y
C. Y + Z
D. X + Y + Z
ANSWER: C
A car travelling at a constant velocity covers a distance of 100 m in 5.0 s. The thrust of the engine is 1.5 kN. What is the power of the car?
ANSWER: 30 kW
The initial kinetic energy of a block moving on a horizontal floor is 48 J. A constant frictional force acts on the block bringing it to rest over a distance of 2 m. What is the frictional force on the block?
ANSWER: 24 N
The efficiency of an electric motor is 20 %. When lifting a body 500 J of energy are wasted. What is the useful work done by the motor?
ANSWER: 125 J
An object, initially at rest, is accelerated by a constant force. Which graphs show the variation with time t of the kinetic energy and the variation with time t of the speed of the object?
ANSWER: A
A stone is falling at a constant velocity vertically down a tube filled with oil. Which of the following statements about the energy changes of the stone during its motion are correct?
The game in kinetic energy is less than the loss in gravitational potential energy
The sum of kinetic and gravitational potential energy of the stone is constant
The work done by the force of gravity, has the same magnitude as the work done by friction
ANSWER: B
A spring of negligible mass and length l₀ hangs from a fixed point. When a mass m is attached to the free end of the spring, the length of the spring increases to l. The tension in the spring is equal to k∆x, where k is a constant and ∆x is the extension of the spring. What is k?
ANSWER: C
A train on a straight horizontal track moves from rest at constant acceleration. The horizontal forces on the train are the engine force and a resistive force which increases with speed. Which graph represents the variation with time t of the power P developed by the engine?
ANSWER: D
The graph shows how the acceleration a of an object varies with distance travelled x. The mass of the object is 3.0 kg. What is the total work done on the object?
1200 J
The Sankey diagram represents the energy flow for a coal-fired power station. What is the overall efficiency of the power station?
ANSWER: 0.3
An electric motor is used to lift a heavy load. The Sankey diagram shows the energy transformations involved in the process. What is the efficiency of the motor?
ANSWER: 75%
A student of mass, m, initially at rest takes seconds to run up stairs of height, h. At the top of the stairs the student has a velocity, v. What is the average power supplied by the student during the climb?
ANSWER: B
An engine provides a thrust force to move a vehicle at constant velocity , v. The engine has an efficiency, e and consumes fuel with an energy density n . Which expression gives the rate at which the volume of fuel is being consumed by the engine?
ANSWER: B
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