1. A constant 10-newton force is applied on a 30-kilogram rollerskater (initiall

Question

1. A constant 10-newton force is applied on a 30-kilogram rollerskater (initially at rest) for 3.0 seconds. How much work in J is done by the force in that time? (Hint: use the kinematic equations to find the distance moved by the rollerskater.)

2. A 1200-kg frictionless roller coaster starts from rest at a height of 24m. What is its kinetic energy when it goes over a spot that is 12 m high?

3. Rocketman is propelled straight up from a cannon with a kinetic energy of 16,000 J. If his mass is 80 kg how high will he fly? (Ignore air friction).

4. A radio-controlled car increases its kinetic energy from 4 J to 12 J over a distance of 2 m. What was the average net force on the car during this interval?

5. Valerie is able to do 1200 joules of work in 10 seconds. Brett is able to do 5000 joules of work in 50 seconds. Who is more powerful?

6. What impulse is needed to bring to a stop a 1400-kg car traveling at 25 m/s?

7. Calculate the time required for a 6000-newton net force to stop a 1200-kilogram car initially traveling at 10 meters per second.

Explanation / Answer

1. The distance, S moved by the rollerskater is calculated as

S = ut + 1/2 at^2

where, u is initial velocity = 0 because body was initially at rest.

Therefore,

S = 1/2 at^2

acceleration, a = Force / Mass = 10 / 30 = 1/3 m/s^2

S = 1/2 at^2 = 0.5*(1/3)*3^2 = 1.5 m

Now the work done, W is calculated as

W = F * S = 10*1.5 = 15 J

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