1.At one instant, a 19.0-kg sled is moving over a horizontal surface of snow at
ID: 1307901 • Letter: 1
Question
1.At one instant, a 19.0-kg sled is moving over a horizontal surface of snow at 3.90 m/s. After 8.95 s has elapsed, the sled stops. Use a momentum approach to find the magnitude of the average friction force acting on the sled while it was moving. N
2.A tennis player receives a shot with the ball (0.060 0 kg) traveling horizontally at 52.0 m/s and returns the shot with the ball traveling horizontally at 43.0 m/s in the opposite direction. (Assume the initial direction of the ball is in the ?x direction.)
(a) What is the impulse delivered to the ball by the tennis racquet?
(b) What work does the racquet do on the ball?
Is the final kinetic energy greater than or less than the initial kinetic energy? J
3.A car of mass m moving at a speed v1 collides and couples with the back of a truck of mass 4m moving initially in the same direction as the car at a lower speed v2. (Use any variable or symbol stated above as necessary.)
(a) What is the speed vf of the two vehicles immediately after the collision?
vf =
(b) What is the change in kinetic energy of the car
Explanation / Answer
Number 1)
8.28 N
Number 2a)
5.7 Ns
Number 2b)
136.6 J
Final KE is less
Number 3a)
mv1 + 4mv2 = 5m(vf)
vf = 2v1 + 8v2
Number 3b)
KEf = .5(5m)(2v1 + 8v2)2
KEi = .5mv12 + .5(4m)(v2)2
Change in KE = 2.5m(2v1 + 8v2)2 - .5m(v12 + 4v22)
If you need this simplified further, that is...
2.5m(4v12 + 32v1v2 + 64v22) - .5m(v12 + 4v22)
That is 9.5mv12 + 80mv1v2 + 158mv22
Number 4)
62 m/s
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