Work and Energy Physics - Work and Energy

Find the average frictional force needed to stop a car weighing 500kg in a distance of 25m if the initial speed is 72km/ h.

A small heavy block is attached to the lower end of a light rod of length l which can be rotated about its clamped upper end. What minimum horizontal velocity should the block be given so that it moves in a complete vertical circle?

A heavy box is kept on a smooth inclined plane and is pushed up by a force F acting parallel to the plane. Does the work done by the force F as the box goes from A to B depend on how fast the box was moving at A and B? Does the work by the force of gravity depend on this?

A block of mass 1kg is placed at the point A of a rough track shown in figure. If slightly pushed towards right, it stops at the point B of the track. Calculate the work done by the frictional force on the block during its transit from A to B.

A block of mass 2.00kg moving at a speed of 10.0m/s accelerates at 3.00m/s² for 5.00s. Compute its final kinetic energy.

A block weighing 10N travels down a smooth curved track AB joined to a rough horizontal surface (figure). The rough surface has a friction coefficient of 0.20 with the block. If the block starts slipping on the track from a point 1.0m above the horizontal surface, how far will it move on the rough surface?

A ball is given a speed v on a rough horizontal surface. The ball travels through a distance l on the surface and stops.

1. What are the initial and final kinetic energies of the ball?
2. What is the work done by the kinetic friction?

Figure shows a light rod of length l rigidly attached to a small heavy block at one end and a hook at the other end. The system is released from rest with the rod in a horizontal position. There is a fixed smooth ring at a depth h below the initial position of the hook and the hook gets into the ring as it reaches there. What should be the minimum value of h so that the block moves in a complete circle about the ring?

A block of mass 250g is kept on a vertical spring of spring constant 100N/m fixed from below. The spring is now compressed to have a length 10cm shorter than its natural length and the system is released from this position. How high does the block rise? Take g =10m/s².

A small block of mass 100g is pressed against a horizontal spring fixed at one end to compress the spring through 5.0cm (figure). The spring constant is 100N/m. When released, the block moves horizontally till it leaves the spring. Where will it hit the ground 2m below the spring?

A box is pushed through 4.0m across a floor offering 100N resistance. How much work is done by the resisting force?

In one of the exercises to strengthen the wrist and fingers, a person squeezes and releases a soft rubber ball. Is the work done on the ball positive, negative or zero during compression? During expansion?

In tug of war, the team that exerts a larger tangential force on the ground wins. Consider the period in which a team is dragging the opposite team by applying a larger tangential force on the ground. List which of the following works are positive, which are negative and which are zero?

1. Work by the winning team on the losing team.
2. Work by the losing team on the winning team.
3. Work by the ground on the winning team.
4. Work by the ground on the losing team.
5. Total external work on the two teams.

The US athlete Florence Griffith-Joyner won the 100m sprint gold medal at Seol Olympic 1988 setting a new Olympic record of 10.54s. Assume that she achieved her maximum speed in a very short-time and then ran the race with that speed till she crossed the line. Take her mass to be 50kg.

1. Calculate the kinetic energy of Griffith-Joyner at her full speed.
2. Assuming that the track, the wind etc. offered an average resistance of one tenth of her weight, calculate the work done by the resistance during the run.
3. What power GriffithJoyner had to exert to maintain uniform speed?

When you push your bicycle up on an incline the potential energy of the bicyle and yourself increases. Where does this energy come from?

Consider two observers moving with respect to each other at a speed v along a straight line. They observe a bock of mass m moving a distancel on a rough surface. The following quantities will be same as observed by the two observers.

1. Kinetic energy of the block at time t.
2. Work done by friction.
3. Total work done on the block.
4. Acceleration of the block.

A block of mass m slides down a smooth vertical circular track. During the motion, the block is in:

1. Vertical equilibrium.
2. Horizontal equilibrium.
3. Radial equilibrium.
4. None of these.

The kinetic energy force on the particle continuously increases with time.

1. The resultant force on the particle must be parallel to the velocity at all instants.
2. The resultant force on the particle must be at an angle less than 90° all the time.
3. Its height above the ground level must continuously decrease.
4. The magnitude of its linear momentum is increasing continuously.

A particle is acted upon by a force of constant magnitude which is always perpendicular to the velocity of the particle. The motion of the particle takes place in a plane. It follows that:

1. Its velocity is constant.
2. Its acceleration is constant.
3. Its kinetic energy is constant.
4. It moves in a circular path.

A 250g block slides on a rough horizontal table. Find the work done by the frictional force in bringing the block to rest if it is initially moving at a speed of 40cm/s. If the friction coefficient between the table and the block is 0.1, how far does the block move before coming to rest?

A small block of mass 200g is kept at the top of a frictionless incline which is 10m long and 3.2m high. How much work was required.

1. To lift the block from the ground and put it at the top.
2. To slide the block up the incline? What will be the speed of the block when it reaches the ground.
3. It falls off the incline and drops vertically on the ground.
4. It slides down the incline? Take g = 10m/s².