A key is dropped from a bridge that is 43.0 m above the water. At the moment the

Question

A key is dropped from a bridge that is 43.0 m above the water. At the moment the key is released a model boat is 12.0 m away from the bridge and moving towards the bridge with constant velocity. If the key falls directly into the model boat, calculate the velocity of the boat?



A rifle is aimed horizontally at a target located 37.0 m away. The bullet hits the target 2.1 cm below the aim point. What was the bullet's time of flight?



In the above problem, what was the speed of the bullet as it emerged from the rifle barrel?

Explanation / Answer

A key is dropped from a bridge that is 43.0 m above the water. At the moment the key is released a model boat is 12.0 m away from the bridge and moving towards the bridge with constant velocity. If the key falls directly into the model boat, calculate the velocity of the boat?
time taken by the key to reach water=43=0+1/2*9.8*t*t so t=2.96sec so velocity of the boat* 2.96=12
hence velocity of the boat= 4.05m/sec
A rifle is aimed horizontally at a target located 37.0 m away. The bullet hits the target 2.1 cm below the aim point. What was the bullet's time of flight?
range of the bullet=37-0.021=36.979m


range=2*u*sin45/g *ucos45=u*u*sin2*45/9.8=36.979m u*u*1/9.8=36.979m so u=19.03m/sec hence t=2*19.03 sin45/9.8=2.745sec
In the above problem, what was the speed of the bullet as it emerged from the rifle barrel?
u=19.03m/sec

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